J/ApJ/348/98 J/ApJ/348/98 LMC AGB stars IRAS fluxes N Reid C Tinney J Mould Astrophys. J. 348 98 1990 1990ApJ...348...98R Infrared sources Magellanic Clouds Stars, giant galaxies: stellar content infrared: sources Magellanic Clouds stars: evolution stars: late-type stars: variables: other (long-period variables) We present the results of a search for optically obscured asymptotic giant branch (AGB) stars in the Large Magellanic Cloud (LMC), combining data obtained using the IRAS satellite with near-infrared photographic plate material of a 15deg^2^ region in the northern LMC. Of the 156 IRAS sources that are detected either in separate cross-scans or in more than one passband, 63 have [12-25] colors consistent with their being either stellar photospheres or circumstellar dust shells. Seventeen of these we identify with bright (I_c_<9) foreground stars in our own Galaxy, while a further 17 are associated with red supergiants in the LMC. Of the remaining stars, no more than five are likely to be optically visible AGB stars, while the rest have no obvious optical counterpart. This immediately rules out the presence of sufficient high-luminosity "cocoon" stars to explain the observed deficit of several hundred luminous (M_bol_<-6) AGB stars between the predictions of standard models of AGB evolution and the observed luminosity function. It remains possible that most of the unidentified sources are dusty AGB stars, evolving through a phase of enhanced mass loss toward becoming planetary nebulae. We infer bolometric magnitudes as low as M_bol_~-5 for these sources and suggest that this phase can be triggered at low luminosities, truncating AGB evolution and leading to the observed scarcity of asymptotic giant branch stars with bolometric magnitudes brighter than -6.0mag.

IRAS

TRM TRM designation number=1 TRM (1990ApJ...348...98R) selected sources in the LMC north field. --- RAh Right ascension (1950) h RAm Right ascension (1950) min RAs Right ascension (1950) s DE- Declination sign --- DEd Declination (1950) deg DEm Declination (1950) arcmin DEs Declination (1950) arcsec Scan Information on the scan directions number=2 Information on the scan directions in which each source was detected unambiguously is given. 1: detected in EW scan 2: detected in NS scan 3: detected in both EW and NS scans --- S12 Flux density at 12 {mu}m number=3 Fluxes listed in this table assume a flux distribution which varies as {nu}-1 (see Sec. IV). Blank entries in the S12, S25, S60, or S100 columns imply either that no flux was detected at that wavelength, or that the region was so confused that the source extraction algorithm was unable to extract any flux, or that the flux density measurement is not reliable. Jy S25 Flux density at 25 {mu}m number=3 Fluxes listed in this table assume a flux distribution which varies as {nu}-1 (see Sec. IV). Blank entries in the S12, S25, S60, or S100 columns imply either that no flux was detected at that wavelength, or that the region was so confused that the source extraction algorithm was unable to extract any flux, or that the flux density measurement is not reliable. Jy S60 Flux density at 60 {mu}m number=3 Fluxes listed in this table assume a flux distribution which varies as {nu}-1 (see Sec. IV). Blank entries in the S12, S25, S60, or S100 columns imply either that no flux was detected at that wavelength, or that the region was so confused that the source extraction algorithm was unable to extract any flux, or that the flux density measurement is not reliable. Jy S100 Flux density at 100 {mu}m number=3 Fluxes listed in this table assume a flux distribution which varies as {nu}-1 (see Sec. IV). Blank entries in the S12, S25, S60, or S100 columns imply either that no flux was detected at that wavelength, or that the region was so confused that the source extraction algorithm was unable to extract any flux, or that the flux density measurement is not reliable. Jy PSC See note number=4 Sources marked with a "*" have been associated positionally with an object in the IRAS PSC --- Rej Rejection (Y: yes, N: no) --- Com Comments on rejection number=6 S100: Source was rejected because it had S100>S60>2S25. S60 Source was rejected because it had S60>2S25. S25>> S12 Source was rejected because it had S25>4S12. GC, C, NSO: Source was rejected because it coincided with a globular cluster, open cluster, or clearly nonstellar object on the V or I band Schmidt plates. PN: Source was rejected because it coincided with a planetary nebula (Sanduleak refs). H{alpha}: Source coincided with a knot of Half in the LMC emission-line survey of Davies et al. (1976MmRAS..81...89D) (c), (u): Source extraction algorithm was unable to produce a meaningful flux estimate at that wavelength, due to either (c) source confusion or (u) unselected source; however, it is clear from the IRAS maps that there is sufficient 60 {mu}m or 100 {mu}m flux present to reject the source. 1: TRM 147 showed some weak evidence fro 60 {mu}m flux which was not selected by IPAC source extractor. Since this source had a PSC 60 {mu}m flux greater than its 25 {mu}m flux, it was therefore rejected. The flux conditions were held to be stronger reasons for source rejection, so although a number of sources listed as being rejected on this basis were also coincident positionally with globular clusters, galaxies, etc., only the flux conditions has been listed here. --- Patricia Bauer CDS 1996Sep30 UNKNOWN UNKNOWN Prepared via OCR at CDS. J_ApJ_348_98.xml