英语学习推荐
听写强化训练系统有听写比对,按句停顿,中文翻译、听写错词提示等特色功能.
关注可可英语官方微信,每天将会向大家推送短小精悍的英语学习资料..
VOA慢速英语
VOA常速英语
PBS高端访谈
科学美国人60秒
可可英语官方微信(微信号:ikekenet)
每天向大家推送短小精悍的英语学习资料.
添加方式1.扫描上方可可官方微信二维码。
添加方式2.搜索微信号ikekenet添加即可。当前位置： >>
Dust-enshrouded Asymptotic Giant Branch Stars in the Solar Neighbourhood
Mon. Not. R. Astron. Soc. 000, 000C000 (0000)Printed 1 February 2008A (MN L TEX style ?le v1.4)Dust-enshrouded Asymptotic Giant Branch Stars in the Solar NeighbourhoodEnrico Olivier1 21,2,3, Patricia Whitelock1and Fred Marang1arXiv:astro-ph/ 19 Mar 2001South African Astronomical Observatory, PO Box 9, Observatory, 7935, South Africa email: paw@saao.ac.za. Department of Physics, University of the Western Cape, Private Bag X17, Bellville, 7535, South Africa. 3 Present address: The Research School of Astronomy and Astrophysics, Private Bag, Weston Creek PO, Canberra, ACT, 2611, Australia. email: rickyo@mso.anu.edu.au.1 February 2008ABSTRACTA study is made of a sample of 58 dust-enshrouded Asymptotic Giant Branch (AGB) stars (including 2 possible post AGB stars), of which 27 are carbon-rich and 31 are oxygen-rich. These objects were originally identi?ed by Jura & Kleinmann as nearby (within about 1 kpc of the sun) AGB stars with high mass-loss rates B (M & 10?6 M⊙ yr?1 ). Ground-based near-infrared photometry, data obtained by the IRAS satellite and kinematic data (radial and out?ow velocities) from the literature are combined to investigate the properties of these stars. The light amplitude in the near-infrared is found to be correlated with period, and this amplitude decreases with increasing wavelength. Statistical tests show that there is no reason to suspect any di?erence in the period distributions of the carbon- and oxygen-rich stars for periods less than 1000 days. There are no carbon-rich stars with periods longer than 1000 days in the sample. The colours are consistent with those of cool stars with evolved circumstellar dust-shells. Luminosities and distances are estimated using a period-luminosity relation. Mass-loss rates, estimated from the 60 ?m ?uxes, show a correlation with various infrared colours and pulsation period. The mass-loss rate is tightly correlated with the K ? [12] colour. The kinematics and scale-height of the sample shows that the sources with periods less than 1000 days must have low mass main-sequence progenitors. It is argued that the three oxygen-rich stars with periods over 1000 days probably had intermediate mass main-sequence progenitors. For the other stars an average progenitor mass of about 1.3 M⊙ is estimated with a ?nal white dwarf mass of 0.6 M⊙ . The average lifetime of stars in this high mass-loss AGB phase is estimated to be about 4 × 104 years, which suggests that these stars will undergo at most one more thermal pulse before leaving the AGB if current theoretical relations between thermal interpulse-period and core-mass are correct. Key words:1INTRODUCTIONStars of low to intermediate main-sequence mass, up to about 6-8 M⊙ , will eventually evolve up the Asymptotic Giant Branch (AGB) (Iben & Renzini 1983). At the tip of the AGB, where they combine a low e?ective temperatures (Tef f & 3000 K) with high luminosities (L & 3000 L⊙ ), the ? ? stars pulsate and are subject to rapid mass loss. Typical examples of such stars are the Miras and the OH/IR? stars (e.g. Feast & Whitelock 1987; Habing 1996). Their light output varies on timescales from around one hundred days? A small fraction of OH/IR stars are supergiants, i.e. their progenitors were massive stars. c 0000 RASto well over a thousand days. They also lose mass rapidly (10?7 & M & 10?4 M⊙ yr ?1 ). They follow various period? B ? luminosity relations and are at or near the maximum luminosity they will ever achieve during their evolution. This makes them very useful as distance indicators and as probes of galactic structure. They are also important contributors of dust into the interstellar medium, which may be crucial for the formation of new stars and planets. Jura & Kleinmann (1989 henceforth JK89) identi?ed a group of mass losing AGB stars within about 1 kpc of the sun. In 1989 a monitoring programme of stars in the JK89 sample visible from the southern hemisphere was initiated from SAAO. This entailed obtaining near-infrared photometry at JHKL over a time interval of several years, from2E. A. Olivier et al.Table 1. Infrared SourcesINFRARED SOURCE CHEM. TYPE SPEC. TYPE VARIABLE NAME? NO. OF REF.?which pulsation periods could be determined. The aim of this study was to investigate the physical properties of the sample, in particular variability, colours, mass-loss rates and kinematics, using SAAO photometry together with infrared photometry and kinematic data from the literature. Finally these data are used to estimate the average progenitor mass and lifetime of stars in this high mass-loss phase.2THE SAMPLEJK89 aimed to develop a more quantitative understanding of mass loss from local AGB stars. They identi?ed AGB stars B undergoing heavy mass loss (M & 10?6 M⊙ yr ?1 ), henceforth referred to as dust-enshrouded, within about 1 kpc of the sun, and within ?33? & δ(1950) & 82? . Their selection was based on infrared photometry from the Two Micron Sky Survey, IRAS and the AFGL survey from which they identify 63 sources. They give reasons for thinking this sample was reasonably complete. A few comments should be made at this point. JK89 assume a luminosity of 104 L⊙ for all of these AGB stars. It will be seen later that, if the period luminosity relation (PL) is correct, this leads to the inclusion of more luminous OH/IR stars outside the 1 kpc sphere and up to ? 2 kpc away. They note that some red supergiants will satisfy thei those they largely excluded, but included the star 3 Puppis, an A supergiant, with the idea that it might be undergoing the transition from AGB star to planetary nebula. However, Plets, Waelkens & Trams (1995) convincingly showed that 3 Puppis is a genuine massive supergiant, and we therefore exclude it from this study. JK89 also included the carbon-rich planetary nebulae NGC 7027 (e.g. Justtanont et al. 2000) this object is excluded from the present study. The remaining 61 sources are listed in Table 1 (this includes 3 M supergiants, , 18135 ? 1641 and 18204 ? 1344 (Ukita & Goldsmith 1984; Winfrey et al. 1994) of which we only became aware part the way through this project). Near-infrared data are tabulated for two of them, but none are used in the analysis. Chemical types (O and C for oxygen- and carbon-rich, respectively) for all the sources were taken from Loup et al. (1993), and spectral types obtained from the SIMBAD data base for 51 of the sources are also listed in Table 1. Although 04307 + 6210 is listed as M6 in SIMBAD, Groenewegen (1994) suggests this is incorrect and the star is
therefore no spectral type is assigned to it here. The supergiants are marked (I). The ?nal sample thus consists of 27 carbon-rich stars and 31 oxygen-rich stars (excluding the 3 supergiants) of which 2 are S-type. Almost all of the stars are of very late spectral type (M, C, N, R and S), with two exceptions: the Red Rectangle and the Egg Nebula. Both are well-known carbon-rich bipolar re?ection nebulae (see, e.g. Sahai et al. 1998; Waters et al. 1998). The Red Rectangle is a wide binary system with an oxygen-rich dust disk (Waters et al. 1998). These two objects are generally thought to be postAGB stars on their way to become Planetary Nebulae. The Benson et al. (1990) catalogue lists sources which have been examined for OH, SiO and H2 O maser emission. Of the 28 oxygen-rich stars in our sample which have beenIRAS 00042 + 4248 IRAS 01037 + 1219 IRAS 01159 + 7220 IRAS 02270 ? 2619 IRAS 02316 + 6455 IRAS 02351 ? 2711 IRAS 03229 + 4721 IRAS 03507 + 1115 IRAS 04307 + 6210 IRAS 04566 + 5606 IRAS 05073 + 5248 IRAS 05411 + 6957 IRAS 05559 + 7430 IRAS 06176 ? 1036 IRAS 06300 + 6058 IRAS 06500 + 0829 IRAS 08088 ? 3243 IRAS 09116 ? 2439 IRAS 09429 ? 2148 IRAS 09452 + 1330 IRAS 10131 + 3049 IRAS 10491 ? 2059 IRAS 12447 + 0425 IRAS 17049 ? 2440 IRAS 17119 + 0859 IRAS 17297 + 1747 IRAS 17360 ? 3012 IRAS 17411 ? 3154 IRAS 17513 ? 2313 IRAS 18009 ? 2019 IRAS 18040 ? 0941 IRAS 18135 ? 1641 IRAS 18194 ? 2708 IRAS 18204 ? 1344 IRAS 18240 + 2326 IRAS 18333 + 0533 IRAS 18348 ? 0526 IRAS 18349 + 1023 IRAS 18397 + 1738 IRAS 18398 ? 0220 IRAS 18413 + 1354 IRAS 18560 ? 2954 IRAS 19008 + 0726 IRAS 19059 ? 2219 IRAS 19093 ? 3256 IRAS 19126 ? 0708 IRAS 19175 ? 0807 IRAS 19321 + 2757 IRAS 20077 ? 0625 IRAS 20396 + 4757 IRAS 20440 ? 0105 IRAS 20570 + 2714 IRAS 21032 ? 0024 IRAS 21286 + 1055 IRAS 21320 + 3850 IRAS 21456 + 6422 IRAS 23166 + 1655 IRAS 23320 + 4316 IRAS 23496 + 6131 RAFGL 1406 RAFGL 2688O O O C O O C O C O O O O C O O C C O C C C C C O O O O O O C O C O C O O O C C O O C O O O C C O C O C C O C O C C O C CM10 M9 Se M9 M9 C M6e M8.5 M M9 M7 B8V M9 M9 C M9 C Ce C Re M9 M2KU And WX Psc S Cas R For V656 Cas UU For V384 Per IK Tau TX Cam NV Aur BX Cam V Cam (Red Rectangle) AP Lyn GX Mon V346 Pup IW Hya CW Leo RW LMi V Hya RU Vir V2108 Oph V833 Her V1019 Sco V774 Sgr V4120 Sgr FX SerM5(I) M8 C M5(I) M8(I) C M M9 C C M7 M9 R M8 M9 S C C M N M9 Ce Ce M7e C M6 C M9 F5IaeNX Ser V437 Sct V1111 Oph V821 Her V1417 Aql V837 Her V3953 Sgr V1418 Aql V3880 Sgr V342 Sgr W Aql V1420 Aql V1965 Cyg V1300 Aql V Cyg FP Aqr RV Aqr UU Peg V1426 Cyg RT Cep LL Peg LP And V657 Cas IY Hya (Egg Nebula)47 216 57 91 39 37 101 277 38 147 120 52 72 272 74 52 31 27 74
82 37 51 50 40 31 15 43 43 15 33 39 51 44 164 85 75 46 35 28 43 53 20 97 52 48 73 162 30 35 54 35 72 18 109 98 24 40 347?-Names in brackets are most commonly used. ?-From 1960 to 1999.examined for OH and H2 O, 20 were detected in OH and 20 in H2 O. While 19 of the 21 sources searched for SiO were detected. Interestingly, 4 of the 11 carbon-rich stars which were searched for SiO also had positive detections. We can thus estimate that 70 percent of the oxygen-rich stars have OH and H2 O maser emission and about 90 percent have SiO emission.c 0000 RAS, MNRAS 000, 000C000c 0000 RAS, MNRAS 000, 000C000Table 2. Near-infrared data. The Date is given as JDC. DATE J H K L DATE J H K L DATE J H K L DATE J H K LIRAS 01037 + .57 7.04 3.90 .98 3.84 .00 3.84 .99 3.86 .08 3.92 .27 4.05 .66 5.84 .81 5.90 .80 5.79 .79 5.93 .74 5.89 .76 5.90 .71 5.90 .57 5.78 .81 5.75 .23 5.52 .28 4.88 .78 3.72 .82 3.74 .00 3.90 .32 4.17 .46 4.29 .68 4.43 .94 6.07 .38 5.02 .03 3.97 .60 4.40 .93 4.63 .15 4.82 .21 4.80 .87 3.94 .66 3.74 .53 3.67 .59 4.45 .84 4.63 .09 4.87 .46 5.061.70 1.68 1.69 1.72 1.76 1.92 3.28 3.30 3.34 3.28 3.25 3.26 3.26 3.15 3.11 2.95 2.49 1.65 1.69 1.84 2.12 2.25 2.35 3.34 2.61 1.98 2.35 2.50 2.64 2.40 1.87 1.72 1.67 2.42 2.57 2.73 2.89?0.68 ?0.69 ?0.69 ?0.67 ?0.64 ?0.46 0.63 0.63 0.49 0.56 0.47 0.52 0.47 0.39 0.38 0.23 ?0.09 ?0.69 ?0.60 ?0.47 ?0.22 ?0.07 0.04 0.50 ?0.01 ?0.35 0.01 0.14 0.25 ?0.21 ?0.53 ?0.60 ?0.61 0.18 0.30 0.41 0.36IRAS 01037 + 1219 .....continued .71 5.32 3.04 0.58 .60 3.75 1.74 ?0.58 .57 3.70 1.71 ?0.59 .51 3.64 1.67 ?0.60 .52 3.63 1.68 ?0.56 .57 3.70 1.76 ?0.52 .40 5.22 2.99 0.50 .52 5.30 3.03 0.55 .68 5.43 3.06 0.41 .19 3.34 1.36 ?0.81 .30 3.43 1.45 ?0.73 .41 3.53 1.54 ?0.62 .65 3.73 1.72 ?0.42 .55 5.11 2.65 0.15 .87 4.67 2.33 ?0.10 .74 3.85 1.75 ?0.55 .66 3.76 1.64 ?0.58 .37 3.42 1.44 ?0.59 .88 3.83 1.79 ?0.23 .63 4.38 2.20 0.14 .03 3.89 1.70 ?0.56 .83 3.81 1.63 ?0.62 .39 3.37 1.30 ?0.81 IRAS 02270 ? .45 4.64 2.88 .49 2.87 .20 2.54 .85 2.22 .70 2.06 .72 2.90 .40 2.64 .18 2.51 .49 1.94 IRAS 02351 ? .68 3.32 1.99IRAS 02351 ? 2711 .....continued .63 2.22 1.38 .60 2.21 1.35 IRAS 03507 + .49 1.54 0.05 .61 0.08 .78 0.27 .00 0.40 .18 0.59 .17 0.54 .25 0.61 .39 0.72 .55 0.81 .51 0.82 .13 ?0.09 .09 ?0.18 .05 ?0.32 .06 ?0.32 .53 ?0.02 .59 0.04 .90 0.28 .32 ?0.15 .34 ?0.09 .32 ?0.19 .25 ?0.22 .26 ?0.24 .27 .27 .37 .31 .81 0.89 .68 0.80 .73 0.85 .50 0.77 .48 0.72 .32 0.68 .19 0.550.51 0.50?0.78 ?0.76 ?0.67 ?0.49 ?0.34 ?0.40 ?0.35 ?0.25 ?0.21 ?0.19 ?0.94 ?1.00 ?1.10 ?1.10 ?0.85 ?0.81 ?0.61 ?1.05 ?1.08 ?1.12 ?1.181.54 1.45 1.27 1.05 0.92 1.54 1.34 1.25 0.830.21 0.07 ?0.10 ?0.30 ?0.38 0.12 0.08 ?0.03 ?0.371.240.44?0.32 ?0.41 ?0.34 ?0.45 ?0.43 ?0.48 ?0.57?1.84 ?1.78 ?1.75 ?1.55 ?1.45 ?1.51 ?1.47 ?1.40 ?1.35 ?1.39 ?2.17 ?2.19 ?2.19 ?2.22 ?1.87 ?1.85 ?1.68 ?2.25 ?2.24 ?2.15 ?2.32 ?2.36 ?2.32 ?2.29 ?2.23 ?2.25 ?1.66 ?1.81 ?1.73 ?1.76 ?1.72 ?1.78 ?1.84IRAS 03507 + 1115 .....continued .15 0.56 ?0.56 .87 0.18 ?0.71 .24 0.49 ?0.52 .73 0.87 ?0.30 .25 ?0.30 ?1.14 .33 ?0.26 ?1.11 .33 ?0.23 ?1.09 .58 ?0.05 ?0.94 .92 0.20 ?0.75 .29 0.50 ?0.51 .81 0.89 ?0.28 .68 0.83 ?0.32 .75 0.24 .27 0.00 .16 ?0.40 ?1.26 .46 0.54 ?0.52 .65 0.71 ?0.40 .07 1.02 ?0.17 .28 1.13 ?0.13 .06 0.98 ?0.23 .73 0.79 ?0.38 .73 0.76 ?0.41 .58 0.68 ?0.45 .38 0.56 ?0.52 .40 ?0.24 ?1.13 .77 0.04 ?0.89 .00 0.24 ?0.72 .60 0.68 ?0.38 .96 1.00 ?0.14 .23 1.17 ?0.05 .42 ?0.10 ?1.04 .88 0.14 ?0.83 .00 0.26 ?0.73 .55 ?0.01 ?0.99 .45 ?0.10 ?1.05 .32 ?0.22 ?1.15 .21 ?0.36 ?1.27?1.84 ?1.77 ?1.60 ?1.56 ?2.25 ?2.27 ?2.16 ?2.02 ?1.85 ?1.58 ?1.55 ?1.59 ?1.99 ?2.23 ?2.36 ?1.62 ?1.55 ?1.41 ?1.40 ?1.51 ?1.70 ?1.67 ?1.76 ?1.81 ?2.20 ?1.97 ?1.90 ?1.56 ?1.42 ?1.40 ?2.26 ?1.93 ?1.87 ?2.23 ?2.30 ?2.37 ?2.46Dust-enshrouded AGB stars in the Solar Neighbourhood 34 E. A. Olivier et al.Table 2. ...continued. Near-infrared data. The Date is given as JDC. DATE J H K L DATE J H K L DATE J H K L DATE J H K LIRAS 03507 + 1115 .....continued .21 ?0.42 ?1.33 .23 ?0.42 ?1.32 .42 1.24 ?0.06 .25 1.11 ?0.17 .15 1.10 ?0.16 .52 0.70 ?0.47 .63 0.09 ?0.87 .76 0.78 ?0.33 .09 1.80 0.39 .87 0.16 ?0.87 .37 0.54 ?0.53 .75 0.84 ?0.29 .19 1.21 ?0.01 .59 0.82 ?0.41 .25 0.56 ?0.61 .88 1.64 0.21 .82 1.64 0.21 .89 1.63 0.21 .80 1.03 ?0.24 .41 0.66 ?0.55 .34 0.56 ?0.63 .79 1.49 0.12 .89 1.56 0.14 .68 1.41 0.01 .52 1.35 ?0.04 .48 1.33 ?0.05 .09 1.12 ?0.21 .51 0.50 ?0.61 .12 0.98 ?0.24 .33 1.16 ?0.10 .52 1.32 0 .40 1.23 ?0.11 .80 0.00 ?1.04 .90 0.04 ?1.00 .16 0.26 ?0.82?2.46 ?2.45 ?1.43 ?1.51 ?1.59 ?1.84 ?2.14 ?1.48 ?1.12 ?2.13 ?1.79 ?1.52 ?1.34 ?1.92 ?2.03 ?1.31 ?1.33 ?1.34 ?1.76 ?2.03 ?2.10 ?1.20 ?1.27 ?1.39 ?1.51 ?1.54 ?1.69 ?1.71 ?1.38 ?1.33 ?1.31 ?1.44 ?2.17 ?2.12 ?1.91IRAS 06176 ? .33 6.61 4.95 .70 5.03 IRAS 08088 ? .32 9.67 .95 .77 .43 .40 .46 .62 .42 .45 .85 .73 .203.39 3.441.30 1.316.64 6.35 6.19 5.01 4.98 5.04 6.10 5.92 5.07 6.18 6.97 6.514.24 4.20 4.09 3.02 3.01 3.05 4.05 3.89 3.12 4.05 4.71 4.311.48 1.53 1.56 0.58 0.57 0.64 1.40 1.30 0.66 1.40 1.91 1.62IRAS 09116 ? .50 10.93 .93 10.31 .75 .21 .39 .15 .64 .47 .43 .58 .74 .96 .26 .16 .62 .46 8.65 .037.36 6.77 6.39 6.89 7.07 5.83 5.34 5.18 5.15 5.27 5.46 6.68 6.88 6.86 5.31 4.71 5.773.03 2.68 2.40 2.91 3.11 1.91 1.51 1.36 1.33 1.42 1.65 2.65 2.80 2.78 1.46 1.92 1.97IRAS 09429 ? .62 6.16 4.41 .43 4.55 .46 4.59 .47 4.58 .54 4.64 .39 4.56 .35 4.53 .34 3.80 .05 3.59 .78 3.19 .85 3.27 .95 3.37 .06 3.47 .10 3.50 .22 3.60 .38 3.76 .52 3.91 .49 3.90 .57 3.93 .82 4.14 .17 4.37 .37 4.50 .50 3.90 .37 3.78 .21 3.66 .03 3.51 .91 3.38 .80 3.25 .41 3.76 .51 3.82 .78 4.04 .03 4.24 .56 4.57 .06 3.46 .98 3.41 .95 3.36 .85 3.273.09 3.16 3.18 3.16 3.22 3.15 3.12 2.52 2.33 1.97 2.06 2.15 2.24 2.28 2.36 2.52 2.64 2.63 2.68 2.83 3.02 3.07 2.55 2.44 2.33 2.21 2.08 1.95 2.46 2.51 2.70 2.84 3.05 2.10 2.05 2.01 1.921.46 1.46 1.44 1.43 1.48 1.38 1.34 0.74 0.57 0.34 0.41 0.49 0.58 0.62 0.75 0.88 0.98 0.99 1.00 1.16 1.36 1.29 0.71 0.62 0.51 0.41 0.29 0.20 0.84 0.93 1.07 1.20 0.28 0.20 0.20 0.11IRAS 09429 ? 2148 .....continued .79 3.14 1.80 0.09 .91 3.28 1.93 0.18 .80 4.04 2.66 1.01 .07 4.28 2.85 1.17 .22 4.38 2.94 1.26 .26 4.44 2.98 1.27 .39 4.52 3.05 1.31 .44 4.57 3.06 1.31 .79 3.10 1.75 0.08 .78 3.09 1.75 0.11 .75 3.05 1.72 0.08 .81 3.08 1.76 0.17 .89 3.19 1.87 0.27 .01 3.30 1.96 0.34 .20 3.46 2.14 0.56 .65 4.54 2.92 1.17 .68 3.85 2.36 0.60 .17 3.35 2.01 0.43 .31 3.46 2.10 0.55 .78 3.83 2.41 0.90 .01 4.01 2.56 0.98 .73 4.45 2.79 1.04 .81 3.00 1.65 0.08 .67 2.82 1.51 ?0.02 .06 3.17 1.87 0.43 .41 3.47 2.13 0.71 .61 2.83 1.57 0.06 .56 2.75 1.50 0.00 .17 4.06 2.60 1.05 IRAS 09452 + .45 8.38 5.01 .24 4.85 .39 3.05 .74 3.40 .05 3.69 .45 4.12c 0000 RAS, MNRAS 000, 000C0002.10 1.95 0.28 0.61 0.90 1.33?1.71 ?1.72 ?3.23 ?3.01 ?2.67 ?2.29c 0000 RAS, MNRAS 000, 000C000Table 2. ...continued. Near-infrared data. The Date is given as JDC. DATE J H K L DATE J H K L DATE J H K L DATE J H K LIRAS 09452 + 1330 .....continued .70 4.48 1.70 ?1.94 .83 3.52 0.73 ?2.87 .22 3.96 1.15 ?2.51 .86 4.61 1.81 ?1.91 .58 3.26 0.52 ?3.02 .26 2.95 0.20 ?3.31 .18 2.85 0.09 ?3.42 .77 4.43 1.54 ?2.24 .85 4.49 1.60 ?2.17 .30 5.03 2.13 ?1.68 .60 3.29 0.43 ?3.21 .88 4.67 1.78 ?2.11 .22 5.07 2.19 ?1.68 .49 4.31 1.46 ?2.34 .32 3.11 0.28 ?3.36 .34 3.12 0.29 ?3.32 .20 5.13 2.25 ?1.73 .07 4.97 2.09 ?1.85 .76 3.47 0.57 ?3.18 IRAS 10131 + .54 6.73 3.98 .48 2.85 .35 2.71 .90 4.13 IRAS 10491 ? .49 2.48 0.85 .29 0.72 .03 0.55 .90 0.48 .81 0.37 .75 0.30 .75 0.33 .78 0.34 .74 0.31 .59 0.091.74 0.76 0.65 1.89?0.99 ?1.78 ?1.84 ?0.84?0.33 ?0.37 ?0.53 ?0.58 ?0.64 ?0.68?0.67 ?0.87?1.59 ?1.59 ?1.71 ?1.75 ?1.78 ?1.83 ?1.81 ?1.72 ?1.76 ?2.09IRAS 10491 ? 2059 .....continued .86 0.32 ?0.72 .98 0.42 ?0.64 .01 0.43 ?0.64 .20 0.60 ?0.53 .94 0.44 ?0.59 .80 0.32 ?0.66 .69 0.24 ?0.74 .65 0.20 ?0.76 .58 0.14 ?0.80 .45 0.05 ?0.88 .39 ?0.02 ?0.92 .39 ?0.06 ?0.96 .51 ?0.01 ?0.94 .21 0.63 ?0.48 .12 0.53 ?0.47 .88 0.38 ?0.62 .83 0.34 ?0.65 .80 0.30 ?0.65 .72 0.26 ?0.67 .73 0.27 ?0.63 .62 0.14 ?0.81 .78 0.26 ?0.73 .92 0.39 ?0.65 .22 0.63 ?0.47 .19 0.59 ?0.49 .69 0.26 ?0.68 .81 0.31 ?0.68 .02 0.46 ?0.56 .48 0.88 ?0.20 .42 0.83 ?0.23 .44 0.82 ?0.23 .37 0.77 ?0.28 .20 0.65 ?0.38 .42 .27 0.65 ?0.40 .29 0.66 ?0.39 .27 0.62 ?0.45?1.88 ?1.84 ?1.83 ?1.76 ?1.75 ?1.85 ?1.86 ?1.92 ?1.94 ?2.03 ?2.10 ?2.05 ?2.01 ?1.65 ?1.75 ?1.72 ?1.78 ?1.78 ?1.74 ?1.74 ?1.91 ?1.88 ?1.82 ?1.63 ?1.62 ?1.85 ?1.84 ?1.71 ?1.62 ?1.63 ?1.61 ?1.65 ?1.89 ?1.80 ?1.81IRAS 10491 ? 2059 .....continued .74 ?0.35 .41 0.73 ?1.67 .41 0.73 ?0.36 ?1.66 IRAS 12447 + .24 4.63 2.94 .08 3.42 .90 3.28 .63 3.04 .30 2.74 .22 2.64 .12 2.62 .15 2.52 .22 2.58 .27 3.54 .00 3.34 .95 3.26 .90 3.22 .99 2.35 .60 3.74 .56 3.75 .45 3.63 .28 3.48 .31 3.51 .78 2.97 .62 3.73 .41 2.61 .63 2.78 .31 3.35 .76 3.81 .51 2.66 .70 2.69 .99 3.22 .59 2.74 .15 2.401.71 2.07 1.97 1.77 1.52 1.45 1.43 1.37 1.41 2.22 2.07 2.01 2.00 1.27 2.29 2.30 2.20 2.10 2.11 1.69 2.29 1.40 1.53 1.99 2.35 1.36 1.34 1.97 1.51 1.270.23 0.46 0.41 0.20 ?0.01 ?0.10 ?0.08 ?0.09 ?0.08 0.66 0.47 0.43 0.43 ?0.22 0.71 0.68 0.59 0.56 0.53 0.17 0.73 ?0.15 ?0.06 0.41 0.74 ?0.20 ?0.20 0.44 0.09 ?0.19IRAS 17049 ? .50 7.66 .15 .35 .65 .56 .60 .46 .18 .63 .28 .94 .53 .32 .56 9.32 .29 IRAS 17119 + .42 4.51 3.16 .38 3.89 .79 3.44 IRAS 17297 + .41 9.87 6.84 .30 5.27 .26 5.21 IRAS 17360 ? .52 9.58 6.36 .50 7.28 .24 7.05 .73 5.78 .87 5.06 .83 5.02 .97 5.12 .38 6.414.73 5.15 5.34 5.61 6.45 6.38 6.25 6.08 5.53 5.28 4.95 4.57 5.34 6.36 6.371.24 1.56 1.76 1.89 2.65 2.62 2.51 2.39 1.91 1.76 1.44 1.13 1.80 2.73 2.71Dust-enshrouded AGB stars in the Solar Neighbourhood2.25 2.65 2.270.81 0.95 0.624.50 2.92 2.881.45 0.08 0.084.36 5.03 4.84 3.76 3.16 3.14 3.27 4.482.12 2.36 2.20 1.37 0.93 0.95 1.07 2.1356 E. A. Olivier et al.Table 2. ...continued. Near-infrared data. The Date is given as JDC. DATE J H K L DATE J H K L DATE J H K L DATE J H K LIRAS 17411 ? .48 13.17 11.01 00.42 03.60 59.61 91.49 IRAS 18009 ? .60 3.86 2.13 IRAS 18040 ? .55 5.83 .87 .77 .72 .10 .37 IRAS 18135 ? .59 2.99 .02 .06 .05 .04 .96 .94 .95 IRAS 18194 ? .57 10.35 .27 31.26 9.88 .469.74 9.643.43 3.44 3.61 3.64 3.90 3.99 4.47 4.29 3.41IRAS 18194 ? .51 8.47 .47 .50 .75 .99 .87 .37 .44 .11 .31 IRAS 18204 ? .58 2.87 .90 .94 .94 .97 .98 .92 .95.....continued 5.33 3.03 5.34 3.03 5.44 3.15 5.57 3.22 5.85 3.49 6.74 4.28 6.26 3.87 6.23 3.85 5.99 3.61 5.19 2.990.32 0.33 0.40 0.54 1.51 1.14 1.11 0.84 0.371.120.113.45 3.48 4.34 4.29 3.76 4.831.79 1.84 2.56 2.55 2.11 3.01?0.05 0.58 0.59 0.23 0.961.31 1.33 1.38 1.38 1.42 1.42 1.39 1.400.61 0.62 0.67 0.70 0.73 0.74 0.72 0.69?0.18 ?0.17 ?0.14 ?0.09 ?0.10 ?0.09 ?0.11 ?0.09IRAS 18333 + 0533 .....continued .27 7.41 4.63 1.96 .35 5.63 3.26 0.82 .17 5.48 3.15 0.78 .00 5.32 3.05 0.70 .00 5.32 3.04 0.68 .90 5.20 2.94 0.68 .52 5.73 3.50 1.25 .31 6.28 3.87 1.52 .10 6.79 4.18 1.73 .15 6.18 3.58 1.03 .68 5.02 2.83 0.62 .14 5.33 3.12 0.98 .07 5.26 2.98 0.71 .07 6.01 3.68 1.48 .34 6.22 3.82 1.59 .10 6.79 4.17 1.76 IRAS 18348 ? .54 52.27 68.56 36.28 09491.52 IRAS 18349 + .65 .00 1.48 .43 1.05 .65 1.18 .87 1.36 .81 2.10 IRAS 18398 ? .63 5.88 3.41IRAS 18398 ? 0220 .....continued .56 4.05 2.21 0.14 .04 3.66 1.95 ?0.08 .60 3.28 1.75 ?0.28 .45 3.14 1.52 ?0.41 .30 3.01 1.40 ?0.50 .26 2.97 1.36 ?0.53 .20 3.79 2.04 0.06 IRAS 18397 + .63 5.34 3.11 .03 2.93 .97 2.85 .01 2.89 .54 4.39 IRAS 18413 + .59 5.01 3.10 .64 2.93 IRAS 18560 ? .65 3.53 2.01 .17 0.94 .29 0.95 .66 1.29 .16 2.47 .18 2.51 .14 1.86 .74 1.53 .94 1.47 .21 1.69 .84 2.15 .13 2.42 .09 0.82 IRAS 19008 + .65 7.51 4.78 .97 4.381.41 1.25 1.20 1.24 2.55?0.62 ?0.81 ?0.83 ?0.77 0.342.08 2.010.99 1.141.57 1.65 1.65 1.65 1.62 1.58 1.56 1.610.93 1.01 0.99 0.99 0.97 0.94 0.93 0.970.14 0.23 0.21 0.22 0.19 0.16 0.17 0.18IRAS 18240 + .59 8.66 .67 .44 .83 8.18 .02 IRAS 18333 + .40 8.79 .64 .50 .42 .50 .81 .52 .035.47 5.42 5.26 4.99 6.721.63 1.54 1.42 1.23 2.637.97 8.32 8.59 9.35 9.74 9.28 7.96 6.772.02 2.28 2.36 2.80 3.03 2.62 1.77 0.947.07 7.01 6.72 6.65 5.364.49 4.46 4.20 4.15 3.031.52 1.50 1.25 0.255.22 5.10 4.99 5.71 5.74 5.96 6.42 6.833.04 2.95 2.89 3.53 3.55 3.70 4.01 4.230.77 0.74 1.36 1.40 1.50 1.70 1.800.60 0.26 0.41 0.52 1.08?0.96 ?0.35 ?0.79 ?0.59 ?0.49 ?0.041.15 0.30 0.30 0.57 1.41 1.45 1.00 0.78 0.73 0.90 1.24 1.40 0.190.06 ?0.60 ?0.48 ?0.25 0.14 0.19 ?0.17 ?0.27 ?0.08 0.03 0.29 0.28 ?0.68c 0000 RAS, MNRAS 000, 000C0001.65?0.332.64 2.340.19 ?0.10c 0000 RAS, MNRAS 000, 000C000Table 2. ...continued. Near-infrared data. The Date is given as JDC. DATE J H K L DATE J H K L DATE J H K L DATE J H K LIRAS 19008 + 0726 .....continued .76 5.09 3.00 0.44 .46 4.80 2.76 0.32 .77 4.18 2.19 ?0.15 IRAS 19059 ? .66 6.06 4.08 .93 2.47 .15 3.48 .87 2.44 .82 2.35 .24 2.85 .13 2.74 IRAS 19093 ? .58 2.61 1.51 .93 1.69 .49 2.16 .77 2.37 .61 1.48 .73 1.54 .25 1.94 .60 1.49 56.27 .69 3.41 2.50 1.46 2.06 1.42IRAS 19126 ? 0708 .....continued .41 0.83 0.08 ?1.08 .63 0.52 ?0.19 ?1.54 .55 0.41 ?1.58 .55 0.41 ?0.31 IRAS 19175 ? .68 7.02 4.17 .51 3.88 .48 5.71 .98 5.16 .21 5.35 .69 4.86 .28 4.48 IRAS 19321 + .60 6.41 4.22 .00 3.63 .14 3.72 .79 4.26 .07 4.52 .71 5.24 IRAS 20077 ? .51 6.84 4.08 .00 4.21 .22 4.37 .27 4.46 .24 3.67 .17 .64 3.13 .50 2.98 .42 2.91 .45 2.91 .10 4.20 .40 4.39 .04 4.92 .87 3.382.78 1.66 2.47 1.64 1.56 1.94 1.851.44 0.66 1.47 0.65 0.66 0.88 0.812.06 1.99 3.52 2.95 3.12 2.68 2.35?0.32 ?0.30 0.89 0.42 0.53 0.20 ?0.02IRAS 20077 ? 0625 .....continued .85 3.34 1.66 ?0.26 .65 3.12 1.49 ?0.36 .83 4.71 2.73 0.77 .02 4.89 2.85 0.81 .44 5.17 3.02 0.87 .60 3.04 1.43 ?0.39 .72 3.14 1.55 ?0.21 .87 3.29 1.68 ?0.07 .97 3.38 1.77 0.04 .30 5.07 2.95 0.85 IRAS 20440 ? .49 2.24 1.23 .28 1.25 .17 2.17 .82 2.48 IRAS 20570 + .67 8.26 5.31 .56 6.59 IRAS 21032 ? .61 5.34 3.26 .50 2.57 .42 3.38 .23 3.25 .43 3.32 .20 3.12 .86 2.07 IRAS 21286 + .31 4.43 2.97 .34 2.94 .08 1.87 .35 2.00 .63 2.19 .16 2.66IRAS 21286 + 1055 .....continued .05 3.51 2.50 1.35 IRAS 23166 + .699.89Dust-enshrouded AGB stars in the Solar Neighbourhood0.92 1.03 1.41 1.58 0.87 0.92 1.27 0.89 0.86 1.36 0.870.03 0.29 0.63 0.74 0.05 0.16 0.56 0.09 0.17 0.67 0.112.55 1.88 1.95 2.39 2.60 3.230.63 ?0.20 ?0.13 0.19 0.33 0.740.81 0.82 1.60 1.770.27 0.80 1.022.97 4.070.23 1.05IRAS 19126 ? .00 3.04 1.51 .44 1.78 .24 2.02 .94 1.41 .77 1.29 .74 2.26 .50 1.74 .22 1.69 .32 0.770.54 0.81 1.12 0.52 0.36 1.40 0.88 ?0.09 0.03?1.21 ?0.81 ?0.70 ?1.18 ?1.22 ?0.04 ?0.22 ?1.30 ?1.172.29 2.39 2.53 2.59 1.88 1.47 1.42 1.32 1.26 1.29 2.39 2.49 2.83 1.690.33 0.43 0.55 0.61 ?0.11 ?0.41 ?0.49 ?0.55 ?0.49 0.60 0.66 0.72 ?0.281.75 1.20 1.90 1.79 1.82 1.66 .850.06 ?0.38 0.32 0.25 0.27 0.09 ?0.591.99 1.96 1.14 1.25 1.42 1.790.93 0.82 0.26 0.39 0.56 0.8278E. A. Olivier et al.3.2.2 Low Resolution Spectra (LRS)From the number of references listed in Tables 1, CW Leo stands out as the best studied source in this sample. About 50 molecular species have been detected in its envelope (Wallerstein & Knapp 1998) which is more than for any other source. The full sample consists mainly of cool variable stars with a few possible post-AGB objects.3 3.1OBSERVATIONS Near-infrared PhotometryThe IRAS Low Resolution spectral classi?cations, from Olnon & Raimond (1986) or Loup et al. (1993), are listed in Table 4. Note that 18135 ? 1641 does not have a published classi?cation so we examined the spectrum in the IRAS Low Resolution Spectra electronic database at the University of Calgary. It shows a weak 10?m emission feature, but no 18?m feature, which is present in the spectra of all the other oxygen-rich stars. It is actually a supergiant as discussed below (section 4).Near-infrared observations were obtained in the JHKL bands (1.2, 1.65, 2.2 and 3.45?m) for 42 of the 45 southern sources, de?ned henceforth as stars with δ & +30? . Some of these 42 stars were selected exclusively from JK89, while the others were already part of other monitoring programmes. The remaining three southern stars (, 17513 ? 2313 and RAFGL 1406) were not observed because they were in crowded ?elds and confusion rendered observations with a single channel photometer impossible (note that Winfrey et al. (1994) suggest that 17513 ? 2313 is actually a supergiant and it is therefore not referred to again). The near-infrared observations for the 42 southern sources, accurate to ±0.1 mag and better (0.03 mag in JHK and 0.05 mag in L in the majority of cases), are listed in Table 2. The magnitudes from the 0.75 m re?ector are on the SAAO system as de?ned by Carter (1990). The HKL bands for the 1.9 m re?ector are assumed to be identical to those of the 0.75 m re?ector, while the J-magnitude is converted to the SAAO system. In some instances, no observations are listed because the sources were too faint to be reliably measured through the relevant ?lter with a particular telescope. The times of the observations are given as Julian dates from which 244 0000 days has been subtracted. In addition to the data from Table 2, published SAAO observations from Whitelock et al. (a) and Lloyd Evans (1997) have been used in the analysis, together with several unpublished observations from Lloyd Evans (private communication) with a sum total of 848 measurements. Mean magnitudes calculated from the average of observed values at maximum and minimum light are listed in Table 3 and compared with the Fourier mean in appendix A. These two averages compare fairly well, di?erences were less than 0.3 mag for the J-band and less than about 0.1 mag for the HKL bands. Table 3 also lists mean K-magnitudes calculated as above from values listed in the literature, for the 20 remaining stars with no near-infrared SAAO photometry. 3.2 3.2.1 Mid- and Far-infrared Observations Photometry4VARIABILITYUsing the data in Table 2, the southern sources were classi?ed as variable in the near-infrared if the di?erence between the maximum and minimum magnitudes at K and/or at L was greater than 0.1 thirty seven of the stars are variable and 2 non-variable. The only two decisively nonvariable stars, 18135 ? 1641 and 18204 ? 1344, are the supergiants (see section 2). There were insu?cient observations to determine if the other 6 stars are variable or not. Table 5 lists the variability information. Period determinations, using Fourier transforms of the K light curve, were made for all variables with measurements on at least 10 epochs. Plausible, although not de?nitive, periods were also established for some sources with as few as 8 measurements. For the very red source , a period could only be estimated from the L data. Periods, listed in Table 5, were thus determined for a total of 20 stars, and phased K light curves for these are shown in Fig. 1. Where possible the Fourier transform analysis was carried out at the other wavelengths and in all cases the periods found were within 2 percent of those listed in Table 5. No period determination was possible for
(W Aql), although it had been observed on 12 epochs. This is because 6 of the epochs were between 1968 and 1982 when this carbon star was undergoing a dust obscuration episode (Mattei & Foster 1997). Such an event would disrupt the apparent periodicity. The average of periods found in the literature are listed in Table 5, with references, for the 47 stars concerned. Where there are periods in common none of them di?ers signi?cantly from those determined here. In the following analysis our own determinations, where available, are used in preference to others, except for 17360 ? 3012 and 18348 ? 0526 where our determination is uncertain due to the small number of measurements available. 4.1 Phased Light-curvesInfrared ?uxes at 12, 25 and 60?m were taken from the IRAS Point Source Catalog (PSC) and colour corrected as speci?ed in the IRAS Explanatory Supplement (ES). The results are listed in Table 4 together with the IRAS ?ux-quality designations and the IRAS variability index (V.I.), which gives the probability that the source is variable in units of 0.1 (see IRAS ES). Table 4 also contains 11?m magnitudes from the Revised Airforce Geophysics Laboratory, RAFGL, survey.Using the periods found for these 20 stars, the relative data were phased, arbitrarily assuming zero phase at JD , where JD is the heliocentric Julian date. These phased light-curves are plotted in Fig. 1 together with least squares ?ts to the data of the form:c 0000 RAS, MNRAS 000, 000C000c 0000 RAS, MNRAS 000, 000C000Table 3. Average near-infrared magnitudesNAME IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS IRAS 00042 +
? 0941JHK 2.52? 2.32 2.30? 1.42 3.10? 0.98 1.65? ?0.47 1.80? ?0.50? 2.95? 1.05? 1.49? 3.41 1.05? 1.07? 3.86 6.03 2.36 1.17 1.27 ?0.09 1.81 5.51 2.45 3.69 4.09 9.69 1.12 2.40LNAME IRAS 18194 ? 2708 IRAS 18240 + 2326 IRAS 18333 + 0533 IRAS 18348 ? 0526 IRAS 18349 + 1023 IRAS 18397 + 1738 IRAS 18398 ? 0220 IRAS 18413 + 1354 IRAS 18560 ? 2954 IRAS 19008 + 0726 IRAS 19059 ? 2219 IRAS 19093 ? 3256 IRAS 19126 ? 0708 IRAS 19175 ? 0807 IRAS 19321 + 2757 IRAS 20077 ? 0625 IRAS 20396 + 4757 IRAS 20440 ? 0105 IRAS 20570 + 2714 IRAS 21032 ? 0024 IRAS 21286 + 1055 IRAS 21320 + 3850 IRAS 21456 + 6422 IRAS 23166 + 1655 IRAS 23320 + 4316 IRAS 23496 + 6131 RAFGL 1406 RAFGL 2688J 9.33 11.83 10.38 3.12 5.76 5.91 4.83 3.13 7.27 4.94 3.14 2.65 7.49 6.86 6.93 3.03 8.91 4.65 4.06H 6.13 9.10 6.20 1.57 3.62 3.51 3.01 1.67 4.63 3.21 1.90 1.33 4.79 4.44 4.04 1.85 5.95 2.72 2.69K 3.74 5.86 3.73 8.26 0.67 1.87 1.79 2.05 0.82 2.59 2.17 1.22 0.54 2.76 2.55 2.14 0.41? 1.29 3.52 1.37 1.82 1.57? 1.49? 10.50 3.55? 2.40? 1.98? 8.40?L 0.88 1.93 1.29 1.98 ?0.50 ?0.24 ?0.19 1.06 ?0.19 0.14 1.06 0.39 ?0.81 0.28 0.27 0.16 0.64 0.64 ?0.13 0.818.06 4.57 2.92 2.574.71 2.74 1.67 0.69?0.09 ?0.06 0.19 ?1.79Dust-enshrouded AGB stars in the Solar Neighbourhood6.654.991.308.57 13.20 5.65 7.28 6.12 2.97 4.88 12.56 4.94 9.07 9.16 13.17 3.86 6.605.97 9.68 3.69 3.99 3.42 1.18 3.08 8.57 3.52 6.02 6.15 11.01 2.13 4.141.24 2.22 0.73 ?2.55 ?1.34 ?1.66 0.26 1.93 0.78 0.76 1.64 3.94 0.11 0.4514.584.27? from Jones et al. (1990) ? from Gezari et al. (1993)910E. A. Olivier et al.Table 4. Mid-infrared and IRAS Data. NAME IRAS 00042 + 4248 IRAS 01037 + 1219 IRAS 01159 + 7220 IRAS 02270 ? 2619 IRAS 02316 + 6455 IRAS 02351 ? 2711 IRAS 03229 + 4721 IRAS 03507 + 1115 IRAS 04307 + 6210 IRAS 04566 + 5606 IRAS 05073 + 5248 IRAS 05411 + 6957 IRAS 05559 + 7430 IRAS 06176 ? 1036 IRAS 06300 + 6058 IRAS 06500 + 0829 IRAS 08088 ? 3243 IRAS 09116 ? 2439 IRAS 09429 ? 2148 IRAS 09452 + 1330 IRAS 10131 + 3049 IRAS 10491 ? 2059 IRAS 12447 + 0425 IRAS 17049 ? 2440 IRAS 17119 + 0859 IRAS 17297 + 1747 IRAS 17360 ? 3012 IRAS 17411 ? 3154 IRAS 18009 ? 2019 IRAS 18040 ? 0941 IRAS 18194 ? 2708 IRAS 18240 + 2326 IRAS 18333 + 0533 IRAS 18348 ? 0526 IRAS 18349 + 1023 IRAS 18397 + 1738 IRAS 18398 ? 0220 IRAS 18413 + 1354 IRAS 18560 ? 2954 IRAS 19008 + 0726 IRAS 19059 ? 2219 IRAS 19093 ? 3256 IRAS 19126 ? 0708 IRAS 19175 ? 0807 IRAS 19321 + 2757 IRAS 20077 ? 0625 IRAS 20396 + 4757 IRAS 20440 ? 0105 IRAS 20570 + 2714 IRAS 21032 ? 0024 IRAS 21286 + 1055 IRAS 21320 + 3850 IRAS 21456 + 6422 IRAS 23166 + 1655 IRAS 23320 + 4316 IRAS 23496 + 6131 RAFGL 1406 RAFGL 2688 [11?m] ?2.5 ?3.4 ?2.9 ?2.6 ?2.7 ?2.7 ?3.2 ?4.2 ?1.9 ?4.1 ?2.4 ?3.0 ?1.6 ?2.7 ?3.0 ?2.6 F12?m (Jy) 391.47 .57 198.84 361.10 334.04 427.14 .65 .98 563.75 158.85 455.93 264.31 576.42 285.54 628.22 461.67 0.79 919.06 175.96 719.06 324.24 465.21 213.51 .95 182.34 599.07 620.16 288.52 421.55 594.84 470.03 466.38 166.23 525.14 369.27 231.57 256.29 .20 283.93 .40 159.03 239.33 242.68 130.17 210.50 133.45 741.06 839.03 303.54 F25?m (Jy) 247.39 770.10 140.93 56.09 231.00 174.63 149.05 .34 480.48 228.27 289.84 78.47 394.29 167.48 291.21 117.61 307.23 362.10 .33 349.97 51.15 392.97 228.96 313.32 264.36 .51 65.62 206.06 345.47 259.03 599.56 242.10 186.34 186.65 111.92 251.45 137.45 159.48 156.32 493.44 151.16 132.23 834.80 176.14 86.10 114.64 86.58 80.86 71.32 78.83 659.45 364.60 194.45 F60?m (Jy) 45.29 171.52 20.35 12.39 35.13 23.04 31.05 223.78 13.44 104.89 58.72 39.92 13.53 142.91 36.23 84.73 24.64 65.49 55.34 .87 77.38 10.54 93.88 31.16 57.71 59.27 .04 16.22 55.30 69.67 61.53 398.50 51.50 47.44 40.78 16.59 49.69 29.12 26.54 25.69 86.06 37.83 30.76 170.94 38.25 13.38 24.89 17.40 14.31 16.03 12.76 203.51 87.96 35.38 F.D.U.? BBD BBC BBC BBC BBD BBD CCC BBB EEC CFD BBD EEC CBC BBC BBE CCD BBC BCD BBE CCB CBB BBD BBD CBC DCC BBF CFD BBC BDD BCC FBD BBE BDD BCE BCD BBD FDF CBD FBD BBD CCD BCD BBD BBD CBC BBB BBD BBE BCC BBC ABC CBC CBB BBC BBD AAC LRS CLASS 26 4no? 22 43 2n? 29 44 26 45 27 24 29 24 80 28 28 4n? 42 28 43 04 4n? 44 42 28 14 42 3n? 29 44 43 42 42, 4no? 3n? 26 43 42 29 27 43 28 28 22 43 43 23 44 27 42 45 26 44 28 02 42 27 V.I. 0 1 1 4 1 5 9 0 9 9 9 9 9 1 9 9 8 9 0 9 2 0 0 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 0 9 9 9 9 9 6 1 9 9 9 2 0 9 0 0 2?1.9 ?7.7 ?5.1 ?3.6 ?1.7 ?3.3 ?2.4 ?2.9 ?1.3 ?3.4 ?3.0 ?2.1 ?2.5 ?2.7 ?2.9 ?2.6 ?3.5 ?3.5 ?3.3 ?2.4 ?3.2 ?2.3 ?2.4 ?2.8 ?3.7 ?2.3 ?2.8 ?3.7 ?3.5 ?1.9 ?2.5 ?2.4 ?2.3 ?2.0 ?1.9 ?3.3 ?3.5 ?2.2 ?3.0 ?2.6All stars have LRS classi?cations taken from IRAS Atlas of Low Resolution Spectra (Olnon & Raimond, 1986), except in the cases marked “?”, which were taken from Loup et al. (1993) ?-Flux Density Uncertainty, as explained in the IRAS Explanatory Supplement.c 0000 RAS, MNRAS 000, 000C000Dust-enshrouded AGB stars in the Solar NeighbourhoodTable 5. Variability data NAME IRAS 00042 + 1219 IRAS 01037 + 1219 IRAS 01159 + 7220 IRAS 02270 ? 2619 IRAS 02316 + 6455 IRAS 02351 ? 2711 IRAS 03229 + 4721 IRAS 03507 + 1115 IRAS 04307 + 6210 IRAS 04566 + 5606 IRAS 05073 + 5248 IRAS 05411 + 6957 IRAS 05559 + 7430 IRAS 06176 ? 1036 IRAS 06300 + 6058 IRAS 06500 + 0829 IRAS 08088 ? 3243 IRAS 09116 ? 2439 IRAS 09429 ? 2148 IRAS 09452 + 1330 IRAS 10131 + 3049 IRAS 10491 ? 2059 IRAS 12447 + 0425 IRAS 17049 ? 2440 IRAS 17119 + 0859 IRAS 17297 + 1747 IRAS 17360 ? 3012 IRAS 17411 ? 3154 IRAS 18009 ? 2019 IRAS 18040 ? 0941 IRAS 18194 ? 2708 IRAS 18240 + 2326 IRAS 18333 + 0533 IRAS 18348 ? 0526 IRAS 18349 + 1023 IRAS 18397 + 1738 IRAS 18398 ? 0220 IRAS 18413 + 1354 IRAS 18560 ? 2954 IRAS 19008 + 0726 IRAS 19059 ? 2219 IRAS 19093 ? 3256 IRAS 19126 ? 0708 IRAS 19175 ? 0807 IRAS 19321 + 2757 IRAS 20077 ? 0625 IRAS 20396 + 4757 IRAS 20440 ? 0105 IRAS 20570 + 2714 IRAS 21032 ? 0024 IRAS 21286 + 1055 IRAS 21320 + 3850 IRAS 21456 + 6422 IRAS 23166 + 1655 IRAS 23320 + 4316 IRAS 23496 + 6131 RAFGL 1406 RAFGL 2688 P (days) 645 389 480 469 Plit (days) ,5,6 ,5
5235 VAR Y Y Y Y ?J 2.87 1.06 1.56 1.96 ?H 2.15 0.88 1.24 1.45 ?K 1.69 0.68 0.92 1.08 ?L 1.34 0.55 0.70 0.9411570 670 640 652 530 441 77533,5
4335(Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y2.09 1.82 2.141.74 2.02 1.56 2.201.47 2.03 1.39 2.111.19 1.54 1.35 1.811.401.22 2.250.99 2.130.91 1.811.901.991.771.55 1.11690 795 (1500)1.66 3.001.57 2.081.35 1.48 3.191.20 1.17 2.11 06600 575
45 25 6 41961.25 2.321.09 1.81.93 1.350.75 1.003801.210.98.780.736752.501.881.451.22YREFERENCES-(1) Whitelock et al. (1994); (2) Le Bertre (1993a); (3) Le Bertre(1993b) ; (4) Whitelock et al. (1997a); (5) Kholopov, P.N. (1985)(GCVS); (6) Jones et al. (1990).c 0000 RAS, MNRAS 000, 000C00012E. A. Olivier et al.Figure 1. Phased Light-curvesc 0000 RAS, MNRAS 000, 000C000Dust-enshrouded AGB stars in the Solar NeighbourhoodFigure 1. Phased Lightcurves.....continued.13c 0000 RAS, MNRAS 000, 000C00014M=E. A. Olivier et al.?M sin(φ ? φ0 ) + Mav (1) 2 where M is the magnitude in a particular band, ?M the peak to peak amplitude, φ related to the phase, p, by φ = 2πp and φ0 the phase angle at zero phase. Mav is the mean magnitude. One immediate observation from most of the phased light-curves is that at a given phase there is a range of magnitudes, rather than one sharply de?ned magnitude. This is not, in general, due to observational error, but is contributed to by various e?ects. First, Miras and OH/IR stars are erratic pulsators in the sense that their light curves do not exactly repeat from one cycle to the next at visual or infrared wavelengths (Koen & Lombard 1995; Whitelock, Marang & Feast 2000) Secondly, some stars, particularly carbon stars go through faint phases from time to time due to variable dust obscuration, e.g. 02270 ? 2619 (R For, see Whitelock et al 1997a). Thirdly, a very small number of stars show temporal or long term changes in luminosity, amplitude and/or period, possibly due to evolutionary e?ects (Whitelock 1999 and references therein). Many of the light curves in Fig. 1 show clear departures from simple sinusoids and would be better ?tted by the inclusion of one or two harmonics, in particular, 09429 ? 2148 and 12447 + 0425. The most strikingly odd curve is that of 10491 ? 2059 (V Hya) which is discussed below. 4.1.1 V HyaFigure 2. (a) K light curve of V Hya. (b) data between JD 244 6000 and 244 8250 phased at 530 days.V Hya is a well studied carbon star and semi-regular variable. It has a bipolar circumstellar out?ow, and models invoke rotation of the central star or the presence of a binary companion to explain bipolar out?ows (Barnbaum, Morris & Kahane 1995). Fig. 2a illustrates the light curve for V Hya using K magnitudes measured from SAAO, including material from Lloyd Evans (1997 and private communication) together with the data from Table 2. In addition to the regular pulsation V Hya experienced two faint phases around JD 244 3500 and 244 9500. A Fourier analysis of the K data when the star is bright, between JD 244 6000 and 244 8250 provide a period of 530 days, identical to the value given in the GCVS. Fig. 2b shows the data phased at this period and illustrates the double peak caused by harmonics in the light curve. Knapp et al. (1999) analysed 3260 AAVSO visual magnitude estimates covering almost 35 years. They con?rm and re?ne the very long period found by Mayall (1965) at 6160 ± 400 days. The two faint phases seen in Fig. 2a are consistent with this long period. The amplitudes of these 6160 day variations are at least 2.4, 2.1, 1.7 and 0.7 mag, at JHKL, respectively, while ?V ? 3.5 mag (Knapp et al. 1999). Barnbaum et al. (1995) found evidence for rapid rotation in V Hya, using spectral line broadening analysis. They suggest that the long term variation can be attributed to a coupling between the radial pulsation, with period of 530 days, and the rotation of the star with a very similar period. It is not clear how this interaction would give rise to the very long period without strongly modulating the shorter period, or why it should result in the observed reddening of the star during the faint phases. Lloyd Evans (1997) suggested that the long period maybe the result of obscuration events like those observed in R For. Although the colours would be consistent with this, the regularity of the long period (Knapp et al. 1999) is quite unlike the e?ect observed in R For and this explanation therefore seems unlikely. Knapp et al. (1999) on the other hand, suggest that the long-period dimming of this star is due to a thick dust cloud orbiting the star and attached to a binary companion. Indeed, there is evidence for large numbers of late-type binaries in the LMC (Wood et al. 1999), so this may not be rare occurrence. The colour variations of V Hya are less extreme than those expected from optically thin interstellar dust, but they could be explained by large particles.4.2Period DistributionsThe period distributions for the oxygen- and carbon-rich stars are plotted in Fig. 3. Most of the stars in the sample have periods between 500 and 700 days and almost all have periods between 300 and 900 days. There are only three extreme OH/IR stars with periods in excess of 1000 days. Fig. 3 can be compared with Whitelock et al. (1994) ?g. 8 which shows the period distribution of IRAS selected Miras in the South Galactic Cap. Most of the Cap sample have 150 & P & 450 days, i.e. shorter than the sample under discussion, but longer than optically selected Miras. Longer period Miras have more massive progenitors and are therefore lower scale heights. It is not surprising to ?nd more of them in the solar neighbourhood than in the Galactic Cap. A comparison of the period distributions of the oxygenand carbon-rich stars is instructive. There are no carbonrich stars with periods longer than 1000 days. From Fig. 3 it can be seen that the maximum of the carbon-star period distribution seems to be slightly shifted to longer periods than that of the oxygen-rich stars. A Kolmogorov-Smirnov (KS) test, when applied to these two distributions for periods less than 1000 days, yields a probability that the twoc 0000 RAS, MNRAS 000, 000C000Dust-enshrouded AGB stars in the Solar Neighbourhood15Figure 4. Light-Amplitude vs. pulsation period, the lines show least squares ? ?lled and open circles represent carbon- and oxygen-rich stars, respectively.Figure 3. Period distributionslight amplitude distributions for the carbon- and oxygenrich stars (with P & 1000 days) came from the same parent population at J, H, K and L of 0.25, 0.92, 0.51 and 0.52 respectively. Hence there is no statistical reason to suspect that these carbon- and oxygen-rich stars have signi?cantly di?erent light-amplitudes in the near-infrared.distributions come from the same parent population of 0.40. This probability (& 0.05) implies that there is no signi?cant di?erence in the period distributions for the carbon- and oxygen-rich stars. The KS test cannot be used if the very long period stars are included since it is not very sensitive to di?erences in the tails of the distributions, as is well known. In this case the F-test and then the appropriate version of the student t-test is applied. The F-test gives a probability that the variances of the two distributions are the same of 2.5 × 10?5 , i.e. very unlikely, which is obvious from Fig. 3. The appropriate version of the t-test, which takes di?erences in variances into account, gives a probability that the two distributions have the same mean of 0.24. This probability (& 0.05) implies that there is no statistical evidence for any di?erence in the mean of the two distributions. 4.3 Amplitudes5 5.1COLOURS Average ColoursTable 5 lists the stars for which periods were determined together with their amplitudes, from equation 1, at JHKL. These amplitudes are plotted against period in Fig. 4, where a clear correlation can be seen at all wavelengths. The amplitude clearly decreases with wavelength (see also Feast et al. 1982). Quantitatively, the average amplitudes, relative to that at J are, for H, K and L respectively, 0.84 ± 0.1, 0.69 ± 0.14 and 0.59 ± 0.14. The linear correlation coe?cient between the average relative amplitude and wavelength is ?0.93 with a correlation probability of P rob = 0.07 (using the relative amplitude at J of 1). This probability is considered as marginally signi?cant. The KS test gives the probability for the null hypothesis that thec 0000 RAS, MNRAS 000, 000C000Average near-infrared colours, i.e. consisting of JHKL magnitudes only, were calculated for each star using the magnitudes at the dates of minimum and maximum K-light. This average is compared to a Fourier-?t colour in Appendix A. The two values are quite comparable with mean di?erences for all the near-infrared colours not exceeding 0.1 mag. Note that due to the very small phase coverage of 17411 ? 3154 in the K-band, the derived K ? L colour of this star may not be a good representative of the average K ? L colour. The IRAS colours were obtained using the data in Table 4, where the colour-corrected IRAS ?uxes were converted to magnitudes using the zero points listed in the IRAS-ES. Colours consisting of JHKL and IRAS photometry, were calculated by combining average magnitudes in the JHKL bands (Table 3) with the IRAS magnitudes. For the northern sources and the three non-IRAS sources the average K magnitudes were taken from Table 3, to calculate the K ? [12] colour. For the non-IRAS (carbonrich) sources the average 12?m magnitudes were estimated from the average [11]?[12] = 0.1±0.3 colour for the carbonrich sources and the 11 ?m magnitudes listed in Table 4. All the derived infrared colours are given in Table 6.16E. A. Olivier et al.Table 6. Infrared Colours NAME IRAS 00042 + 4248 IRAS 01037 + 1219 IRAS 01159 + 7220 IRAS 02270 ? 2619 IRAS 02316 + 6455 IRAS 02351 ? 2711 IRAS 03229 + 4721 IRAS 03507 + 1115 IRAS 04307 + 6210 IRAS 04566 + 5606 IRAS 05073 + 5248 IRAS 05411 + 6957 IRAS 05559 + 7430 IRAS 06176 ? 1036 IRAS 06300 + 6058 IRAS 06500 + 0829 IRAS 08088 ? 3243 IRAS 09116 ? 2439 IRAS 09429 ? 2148 IRAS 09452 + 1330 IRAS 10131 + 3049 IRAS 10491 ? 2059 IRAS 12447 + 0425 IRAS 17049 ? 2440 IRAS 17119 + 0859 IRAS 17297 + 1747 IRAS 17360 ? 3012 IRAS 17411 ? 3154 IRAS 18009 ? 2019 IRAS 18040 ? 0941 IRAS 18194 ? 2708 IRAS 18240 + 2326 IRAS 18333 + 0533 IRAS 18348 ? 0526 IRAS 18349 + 1023 IRAS 18397 + 1738 IRAS 18398 ? 0220 IRAS 18413 + 1354 IRAS 18560 ? 2954 IRAS 19008 + 0726 IRAS 19059 ? 2219 IRAS 19093 ? 3256 IRAS 19126 ? 0708 IRAS 19175 ? 0807 IRAS 19321 + 2757 IRAS 20077 ? 0625 IRAS 20396 + 4757 IRAS 20440 ? 0105 IRAS 20570 + 2714 IRAS 21032 ? 0024 IRAS 21286 + 1055 IRAS 21320 + 3850 IRAS 21456 + 6422 IRAS 23166 + 1655 IRAS 23320 + 4316 IRAS 23496 + 6131 RAFGL 1406 RAFGL 2688 J?H 3.51 1.71 1.25 1.96 H?K 2.26 1.33 0.69 1.16 J?K 5.77 3.04 1.94 3.12 K?L 2.48 1.47 0.79 1.32 K ? [12] 5.37 6.26 4.65 3.54 5.87 3.66 4.60 4.81 3.90 3.69 5.22 4.30 3.36 6.43 3.48 4.34 6.37 9.40 5.39 9.09 6.24 3.69 3.80 9.02 5.10 6.73 6.28 13.99 3.78 4.43 7.06 9.21 6.25 11.19 3.98 4.92 4.83 3.97 3.99 5.38 4.45 3.61 4.61 5.46 5.06 6.13 3.60 3.16 5.83 3.71 3.48 3.75 3.17 14.05 7.23 4.98 5.1 11.1 [12] ? [25] 1.06 1.21 0.96 0.19 1.07 0.86 0.42 0.68 0.42 0.45 1.56 0.84 0.79 1.40 1.06 0.82 0.60 0.78 1.30 0.64 0.38 0.51 0.22 0.90 1.18 1.13 1.79 2.14 1.11 0.45 0.40 0.92 1.44 1.94 0.58 0.56 0.57 1.13 0.76 0.49 1.15 1.02 0.60 0.67 0.73 1.24 0.35 0.89 0.76 0.44 1.04 0.38 0.99 1.43 0.66 1.08 [25] ? [60] 0.04 0.25 ?0.22 0.24 ?0.16 ?0.32 0.18 ?0.27 0.12 0.23 0.41 ?0.27 ?0.03 0.78 0.22 0.54 0.18 0.20 ?0.16 0.37 0.29 0.24 0.17 0.33 ?0.28 0.04 0.26 1.04 ?0.07 0.36 0.45 0.14 0.32 1.44 0.20 0.40 0.23 ?0.19 0.12 0.20 ?0.07 ?0.08 ?0.02 0.38 0.30 0.16 0.22 ?0.14 0.22 0.14 0.00 0.26 ?0.10 0.61 0.34 0.031.661.583.242.112.59 1.86 3.20 2.70 1.79 1.85 1.42 3.04 3.01 1.73 2.46 3.20 4.26 1.55 2.14 2.40 1.81 1.47 2.63 1.72 1.31 1.31 2.70 2.42 2.89 1.18 2.96 1.92 1.382.12 3.75 1.34 2.82 2.15 1.27 1.29 3.04 1.08 2.33 2.07 1.02 1.74 2.39 3.24 2.48 0.90 1.74 1.72 0.97 0.84 2.04 1.04 0.70 0.79 2.04 1.89 1.90 0.56 2.43 1.35 0.864.71 3.19 6.02 4.85 3.06 3.15 2.50 5.37 5.08 2.74 4.20 5.59 6.74 2.45 3.88 4.12 2.78 2.31 4.67 2.77 2.01 2.10 4.74 4.31 4.79 1.74 5.39 3.27 2.242.62 3.56 1.62 3.74 2.61 1.55 1.54 3.62 1.57 2.93 2.43 6.25 1.01 1.95 2.80 3.93 2.44 6.27 1.09 2.12 1.98 0.98 1.07 2.45 1.12 0.76 2.46 2.29 1.98 0.65 2.88 1.51 1.016.23c 0000 RAS, MNRAS 000, 000C000Dust-enshrouded AGB stars in the Solar Neighbourhood17Figure 5. J ? H versus H ? K; ?lled circles represent carbonrich stars, open circles oxygen-rich stars and ?ve-point star Stype stars. The solid line represent loci of blackbodies of di?erent temperatures.Figure 7. K-[12] versus [12]-[25]. Symbols as in Fig. 5. Dotted line separates the chemical types and is given by equation 3.pre-planetary nebula with an oxygen-rich circumstellar disk (see section 2.1). The dashed line in Fig. 7 has been positioned so as to separate the carbon- and oxygen-rich stars as far as possible, it is described by: (K ? [12]) = 11.5([12] ? [25]) ? 3.8 Thus if we de?ne δC/O as follows: δC/O = 11.5([12] ? [25]) ? (K ? [12]) ? 3.8, (3) (2)Figure 6. J-K versus K-L. Symbols as in Fig. 5.5.2Colour-Colour DiagramsThe two chemical types can be separated by a single parameter, δC/O , such that for carbon stars δC/O & 0 and for most oxygen-rich stars δC/O & 0. This parameter might be useful for separating these objects over the colour range discussed. On this sample, obviously the one used to de?ne the parameter, only 6 percent of stars were misclassi?ed. The two S-type stars were omitted from the above discussion, we note that one of them falls with the carbon- and the other with the oxygen-rich stars. 5.2.2 IRAS Two Colour DiagramInfrared two colour diagrams are illustrated in Figs. 5 to 8. There is a clear separation of the oxygen- and carbon-rich stars in these diagrams with the carbon stars falling to the lower right of the oxygen-rich stars in the near-infrared two colour diagrams (Figs. 5 and 6) and to the left of them in the combined diagram, Fig. 7. The JHKL colours of these AGB stars are more extreme than those of the well studied Miras (e.g. Feast et al. 1982), or even of IRAS selected Miras in the Galactic Cap (Whitelock et al. 1994).Van der Veen & Habing (1988) demonstrated that the position of an AGB star in an IRAS two-colour diagram, of the type shown in Fig. 8, was indicative of its chemical type and the thickness of its dust shell. Combined with information on variability and IRAS spectral-type the diagram provides a useful diagnostic. The colour indices for this plot (C12/25 , C25/60 ) are de?ned by: C12/25 = 2.5 log( F25?m ), F12?m F60?m ), F25?m5.2.1The K ? [12] versus [12] ? [25] DiagramOf particular interest is the K ? [12] vs. [12] ? [25] diagram (Fig. 7). The colours of the oxygen- and carbon-rich stars separated rather clearly in this diagram. This has been noted previously (Le Bertre et al. 1994) and shown to be the result of the di?erence in the ratios of the near-infrared to midinfrared opacities for the carbon- and oxygen-rich dust. The single carbon star which falls among the oxygenrich stars is
(the Red Rectangle), a well studied, but peculiar star. It has an IRAS LRS classi?cation of 80 indicating the presence of the 11.3?m line in emission in contrast to the other carbon stars which show 11.3?m absorption, hence its position in Fig. 7. It is thought to be ac 0000 RAS, MNRAS 000, 000C000C25/60 = 2.5 log(where the IRAS ?uxes are not colour corrected. Following van der Veen & Habing the diagram is divided into regions, each of which is dominated by a certain type of object. Stars with low mass-loss rates will fall in the lower left of the diagram and increasingly higher mass-loss rates are found as one moves to the upper right. Most of the oxygen-rich stars under discussion occupy region IIIa which van der Veen & Habing found to contain variable stars with moderate oxygen-rich dust-shells.18E. A. Olivier et al.Figure 8. C25/60 versus C12/25 . Symbols as in Fig. 5. 18135 ? 1641 has only an upper limit to its C25/60 colour as indicated by the arrow.Figure 9. BC12 versus K ? [12]. Symbols as in Fig. 5. Curves are those given in equations 4 and 4.Four stars are located in regions IIIb and IV, indicating thick to very thick oxygen-rich dust-shells and high massloss rates. Four oxygen-rich stars are located in region VII, an area dominated by carbon stars, but where van der Veen & Habing also found oxygen-rich stars. Most of the LRS spectra for oxygen-rich stars in this sample are classi?ed as 2n, indicating that the 10?m silicate feature is in emission. The two oxygen-rich variables with the reddest [12] ? [25] colour, 17411 ? 3154 and 18348 ? 0526, have LRS classi?cations of 3n, i.e. their spectra show the 10?m silicate feature in absorption. In these stars the dustshell has become so cool and optically thick that the silicate feature has gone into absorption. Most of the carbon-stars fall in region VII, which is characterised by variable stars with well developed carbonrich dust-shells. All of these stars have an LRS classi?cation of 4n, indicating that the SiC 11?m feature is in emission. The Red Rectangle, 06176 ? 1036, (discussed above) is located in region IIIa, as is . The latter object has an LRS classi?cation of O2, probably due to self absorption of the SiC feature in the very think shell (Loup et al. 1993).which have no measurements in the J and/or H bands, zero ?ux at J and H was assumed when making the spline ?t. To estimate an upper-limit to the amount of ?ux not accounted for by ignoring the tail in the ?ux distribution, a Wien approximation, ?Aν 3 e?bν (where A and b are constants), was assumed for ?ux at frequencies higher than J with the same slope as the spline at J. In more than 75 percent of the cases the di?erence between the ?uxes calculated in this way and the simple spline ?t was less than 1 percent. 20440 ? 0105, which has the smallest K ? [12] = 3.16, shows the maximum di?erence of 5 percent. Neglecting H2 O absorption between the J,H,K and L bands (Robertson & Feast 1981) will have a negligible e?ect on the bolometric magnitude estimated for stars whose ?ux originates largely from the circumstellar dust-shell. The bolometric corrections at 12 ?m, BC12 , is plotted against the K ? [12] colour in Fig. 9, together with curves given by: BC12 = ?15.4e?0.70(K?[12]) + 8.10, and BC12 = ?7.59e?0.43(K?[12]) + 8.41, (5) (4)6 6.1BOLOMETRIC MAGNITUDES AND DISTANCES Apparent Bolometric Magnitudeswhich are least-square ?ts of this form to the oxygen- and carbon-rich star data respectively. The rms di?erence between the data and these curves is 0.04 and 0.06 mag respectively. For the remaining sources mbol was calculated from [12] and K ? [12] using equations 4 and 5. The apparent luminosities derived here are typically rather smaller than those estimated by JK89, because of the colour corrections applied to the IRAS photometry. 6.2 Absolute Bolometric Magnitudes and LuminositiesGiven that these sources were selected on the basis of their high ?uxes and therefore small distances, together with the fact that the bulk of their energy is emitted at infrared wavelengths it is reasonable to assume that the e?ects of interstellar extinction are negligible. The apparent bolometric magnitude, mbol , were calculated by integrating under a spline curve (Hill 1982), ?tted to the J, H, K, L, 12- and 25?m ?uxes as a function of frequency. The end-points were dealt with by extrapolating a line, which joins the J ?ux and the point lying halfway between the H and K ?uxes, to zero ?ux. Zero ?ux at zero frequency was assumed. The derived values of mbol are listed in Table 7 for the sources with su?cient photometry. For the very red sources 23166 + 1655 and 18348 ? 0526,For the 47 stars with periods the absolute bolometric magnitudes, Mbol , was calculated from the period-luminosity (PL) relation, equation 6, derived for LMC variables (Feast et al. 1989) assuming an LMC distance modulus of 18.60 mag (Whitelock et al. 1997b) and the results given in Table 7. Mbol = ?2.34 log P + 1.26 (6)The average luminosity, for all stars with periods less than 1000 days is (0.98 ± 0.17) × 104 L⊙ , or Mbol = ?5.23 ± 0.19. For stars with unknown periods this mean value isc 0000 RAS, MNRAS 000, 000C000Dust-enshrouded AGB stars in the Solar Neighbourhood which seems reasonable since the carbon stars seem to have periods less than 1000 days and the remaining oxygen-rich stars have [12] ? [25] colours suggesting that they too have periods less than a 1000 days. This value of the mean luminosity suggests that the 104 L⊙ often assumed for the luminosity of the tip of the AGB is consistent with the application of the PL relation to this type of AGB star. Note this value may not be applicable to the Red Rectangle and the Egg Nebula, since they may have left the AGB already. It is not really clear at this stage how well the various PL relations ?t long period variables or if di?erent relations should be used for the oxygen- and carbon-rich stars. Provided this caveat is born in mind when the results are interpreted it seems reasonable to use the luminosities derived as described above. Note, in particular, that the PL relation used above was derived for stars with periods less than 420 days and it may not be appropriate to use it for the present sample. There certainly are long period AGB (P & 420 days) stars in the LMC that lie above the PL relation (e.g. Feast et al. 1989). However, recent work on dust-enshrouded stars in the LMC suggest that these AGB stars are over-luminous because they are undergoing hot bottom burning and that more normal long period (P ≥ 400 day) carbon- and oxygenrich AGB stars fall very close to the PL derived for shorter period oxygen-rich stars (Whitelock & Feast 2000). 6.3 Distances19Figure 10. λ? versus K ? [12]. Filled and open circles represent 10 carbon- and oxygen-rich stars, respectively. The arrowed point, the Red Rectangle, is not used in the solution.? Jansky and λ10 the mean wavelength of light emerging from the star and its circumstellar dust-shell in units of 10?m. Equation 7 assumes all the grains have an emissivity of 150 cm2 g?1 at 60?m and a dust to gas ratio of 4.5 × 10?3 (Jura 1986). The mean wavelength of light emerging from ? the star and its circumstellar dust-shell, λ10 , is given by:∞? λ10 =0λFλ dλ Fλ dλ∞(8)0Distances to all the stars in the sample (excluding the Red Rectangle and the Egg Nebula) were calculated from mbol and Mbol and are listed in Table 7. These distances are typically larger than those estimated by JK89. As discussed above the apparent luminosities used here are smaller than JK89’s, while the absolute luminosities are on average the same, except for the 3 stars with P & 1000 where they are brighter. Thus we ?nd sources with distances up to 2 kpc. The other plausible way of estimating distances to OH/IR stars is the phase lag method, although it is notoriously di?cult and time consuming. Van Langevelde, van der Heiden & Schooneveld (1990) measured phase lag distances for two of the stars under discussion. For
(WX Psc) they get 0.74 ± 0.15 kpc, identical to the PL distance given in Table 7. For 18348 ? 0526 (OH26.5+0.6) they give two values, 1.44 ± 0.27 and 1.30 ± 0.35 kpc, both somewhat closer than the 1.9 kpc listed in Table 7. Given the uncertainties in phase lag and the PL method this di?erence is not problematic. West (1998) has measured a phase lag distance for 17411 ? 3154 (OH357.3C1.3) of 1.2 ± 0.4 kpc, in agreement with the distance of 0.99 kpc listed in Table 7.where Fλ the monochromatic ?ux density in units of energy received per unit area per unit time per unit wavelength interval. For the stars for which the function Fν could be es? timated (section 6.1), λ10 was calculated from equation 8 ? and is listed in Table 7. The relationship between λ10 and K ? [12] is illustrated in Fig. 10 and can be expressed as: ? λ10 = c + b(K ? [12]) + a(K ? [12])2 , (9)7MASS-LOSS RATESB Mass-loss rates, M , were estimated using the expression given by Jura (1987):?1/2 2 ? B Fν,60 λ10 , M = 1.7 × 10?7 v15 rkpc L4(7)where v15 is the out?ow velocity of the gas in units of 15 km s?1 , rkpc the distance to the star in kpc, L4 the luminosity in units of 104 L⊙ , Fν,60 the ?ux measured at 60?m inc 0000 RAS, MNRAS 000, 000C000where a, b and c are constants. Least square ?ts of equation 9 to the data results in the following values (a,b,c) for oxygen-rich (C0.,C 0.392) and carbon-rich (C0.,C0.513) stars, respectively, with an rms error of 0.05 ?m for both chemical types. The discrepant carbon star is the Red Rectangle which was omitted from the solution. Equation 9 with the appropriate parameters is used to ? estimate λ10 for the remaining the results are listed in Table 7 The out?ow velocities, v15 , were taken to be the expansion velocities of the shell obtained from CO(1 → 0) line measurements. Appropriate values from the literature are listed in Table 7 with references. For the three stars without measurements an average out?ow velocity, for stars with vout & 25 km s?1 , of 17 ± 4 km s?1 was used. Jones et al. (1983, henceforth JHG) have shown there to be a correlation between out?ow velocity and luminosity for a sample of OH/IR stars (see ?g. 1 in JHG). The out?ow velocity versus luminosity for stars with periods in our sample is illustrated in Fig. 11. It shows no obvious correlation, which should not be entirely unexpected, considering the large spread in out?ow velocity at a given luminosity (up to 10 km s?1 ) in ?g. 1 of JHG and the small range in Mbol in Fig. 11 (compared to that in ?g. 1 of JHG).20E. A. Olivier et al.Table 7. Physical and Kinematic data. NAME IRAS 00042 + 4248 IRAS 01037 + 1219 IRAS 01159 + 7220 IRAS 02270 ? 2619 IRAS 02316 + 6455 IRAS 02351 ? 2711 IRAS 03229 + 4721 IRAS 03507 + 1115 IRAS 04307 + 6210 IRAS 04566 + 5606 IRAS 05073 + 5248 IRAS 05411 + 6957 IRAS 05559 + 7430 IRAS 06176 ? 1036 IRAS 06300 + 6058 IRAS 06500 + 0829 IRAS 08088 ? 3243 IRAS 09116 ? 2439 IRAS 09429 ? 2148 IRAS 09452 + 1330 IRAS 10131 + 3049 IRAS 10491 ? 2059 IRAS 12447 + 0425 IRAS 17049 ? 2440 IRAS 17119 + 0859 IRAS 17297 + 1747 IRAS 17360 ? 3012 IRAS 17411 ? 3154 IRAS 18009 ? 2019 IRAS 18040 ? 0941 IRAS 18194 ? 2708 IRAS 18240 + 2326 IRAS 18333 + 0533 IRAS 18348 ? 0526 IRAS 18349 + 1023 IRAS 18397 + 1738 IRAS 18398 ? 0220 IRAS 18413 + 1354 IRAS 18560 ? 2954 IRAS 19008 + 0726 IRAS 19059 ? 2219 IRAS 19093 ? 3256 IRAS 19126 ? 0708 IRAS 19175 ? 0807 IRAS 19321 + 2757 IRAS 20077 ? 0625 IRAS 20396 + 4757 IRAS 20440 ? 0105 IRAS 20570 + 2714 IRAS 21032 ? 0024 IRAS 21286 + 1055 IRAS 21320 + 3850 IRAS 21456 + 6422 IRAS 23166 + 1655 IRAS 23320 + 4316 IRAS 23496 + 6131 RAFGL 1406 RAFGL 2688 mbol (4.89) 4.00 (5.16) 4.64 (5.08) 4.21 (4.39) 2.35 (4.87) (2.75) (5.44) (4.09) (4.77) 4.99 (4.33) (4.09) 5.45 4.94 4.75 0.38 2.96 3.04 4.93 4.77 4.97 4.91 5.65 3.80 4.38 5.21 4.80 4.92 5.38 5.13 3.81 4.41 4.42 5.25 3.98 4.80 5.16 4.44 3.36 4.91 4.96 3.99 (3.58) 4.58 5.31 4.55 5.10 (4.69) (4.75) 4.72 (4.38) (5.05) (4.45) Mbol ?5.51 ?5.35 ?5.30 ?4.84 ?5.16 ?5.05 ?5.17 ?5.03 ?5.23 ?5.21 ?5.33 ?5.23 ?5.14 ?5.23 ?5.15 ?5.23 ?5.39 ?5.35 ?5.37 ?5.35 ?5.16 ?4.97 ?5.54 ?5.23 ?5.14 ?5.94 ?6.17 ?5.23 ?5.23 ?5.42 ?5.23 ?5.57 ?6.26 ?5.10 ?5.12 ?5.28 ?5.26 ?5.24 ?5.24 ?5.12 ?4.82 ?5.08 ?5.40 ?5.32 ?5.40 ?4.92 ?5.23 ?5.51 ?5.00 ?5.00 ?5.03 ?5.32 ?5.44 ?5.31 ?4.92 ?5.23 D (kpc) 1.20 0.74 1.24 0.79 1.12 0.71 0.82 0.30 1.05 0.39 1.43 0.73 0.96 0.82 0.70 1.37 1.17 1.05 0.14 0.46 0.44 0.95 1.15 1.10 1.02 2.08 0.99 0.84 1.22 1.11 1.07 1.55 1.90 0.60 0.81 0.87 1.27 0.70 1.02 1.14 0.71 0.49 1.16 1.14 0.76 0.50 0.92 1.46 0.81 1.05 0.88 1.03 1.08 0.87 0.98 0.86 ?10 λ (0.91) 1.06 (0.76) 0.49 (1.00) 0.51 (0.68) 0.79 (0.55) (0.55) (0.88) (0.69) (0.47) 1.17 (0.50) (0.70) 0.98 1.29 0.97 1.26 0.93 0.52 0.53 1.29 0.85 1.06 1.16 1.58 0.59 0.64 1.06 1.29 1.09 1.44 0.58 0.72 0.72 0.64 0.59 0.78 0.75 0.51 0.68 0.80 0.74 1.11 (0.49) 0.41 0.83 0.53 0.51 (0.52) (0.42) 1.43 (1.09) (0.83) (0.75) vout (km s?1 ) 21.7 21.6 21.4 20.0 15.4 16.2 15.3 22.0 18.8 18.7 18.0 21.2 15.1 01.6 16.8 20.0 20.7 13.4 14.0 15.0 16.9 14.2 16.9 20.7 14.0 17.0 20.0? 20.5 17.0? 22.0 23.0 15.1 20.0 10.6 17.0 15.6 34.5 18.5 13.2 17.4 22.2 15.0 19.9 35.5 24.4 16.0 13.7 10.8 23.5 16.1 13.5 14.0 17.0 14.5 14.6 19.0 10.9 19.0 B Log(M) ?4.87 ?4.64 ?5.19 ?5.82 ?5.10 ?5.77 ?5.51 ?5.31 ?5.62 ?5.59 ?4.66 ?5.37 ?5.82 ?5.48 ?5.08 ?4.97 ?4.84 ?5.05 ?4.79 ?5.10 ?5.74 ?5.82 ?4.54 ?5.26 ?4.90 ?4.34 ?3.67 ?5.42 ?5.31 ?4.77 ?4.80 ?4.52 ?3.89 ?5.52 ?5.31 ?5.00 ?5.36 ?5.55 ?5.28 ?5.10 ?5.72 ?5.39 ?4.77 ?5.04 ?4.76 ?5.92 ?6.05 ?4.94 ?5.77 ?5.72 ?5.80 ?5.77 ?4.37 ?4.95 ?5.11 (?5.14) B Log(Mmodel )? ?4.62 ?4.92 ?5.46 ?5.82 ?4.96 ?5.59 ?5.26 ?5.35 ?5.10 ?5.52 ?5.24 ?5.00 ?5.85 ?5.26 ?5.21 ?5.20 ?4.92 ?5.43 ?4.32 ?5.12 ?5.08 ?4.54 ?4.80 ?5.06 ?4.92 ?5.03 ?4.82 ?4.80 ?5.26 ?5.04 ?4.77 ?5.19 ?5.09 ?5.21 ?4.89 ?5.07 ?5.24 ?4.66 ?4.89 ?5.52 ?5.40 ?5.35 ?5.42 ?5.55 ?5.64 ?4.68 ?4.68 vlsr (km s?1 ) ?19.0 ?50.1 9.9 ?68.1 4.5 ?66.5 ?7.6 ?31.4 9.9 8.6 7.8 20.1 22.9 ?11.7 21.5 4.1 0.4 16.2 23.3 45.1 56.0 33.6 67.0 9.3 ?0.8 25.3 0.5 ?1.3 0.8 5.3 ?6.2 15.8 6.0 0.6 7.8 10.0 1.0 8.0 ?14.7 0.8 ?13.6 ?18.4 ?8.5 ?10.0 4.0 ?20.3 3.8 ?25.8 ?12.0 ?29.6 ?28.2 ?9.4 21.0 ?40.4 ?17.1 ?0.3 33.9 ?6.5?3.85? - model mass-loss rates taken from Loup et al. (1993). Almost all stars have out?ow velocities taken from Loup et al. (1993), with the following exceptions: ?