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Searches for OH masers in the circumstellar envelopes of red giant irregular variable stars
Irregular variables of type Lb share many characteristics withasymptotic giant branch (AGB) stars such as Miras and semiregulars(SRs). Despite their large number, irregulars are poorly understood.Using the large Nançay radio telescope, we searched for 18-cm OHmaser emission from these stars. We selected two samples of Lbs thatpresent a noticeable circumstellar envelope. In the first one, 44high-latitude objects with infrared colours of dusty mass-losing starswere observed in a wide-bandwidth velocity-search mode. In addition, 16objects (including six from the first sample), in which othercircumstellar molecular lines had recently been found, were observedwith higher resolution and sensitivity. We did not detect any new OHmaser emission from these samples down to 3σ sensitivity limitsranging from 30 to 200 mJy. We derived upper limits for the efficiencyof a typical pump using far-infrared photons. When compared with knownOH masers in AGB stars, we show that a significant gap is leftunexplored below the threshold that we determined for Lbs. Lowerefficiencies exist in some OH Miras and in the OH SRs. We cannot discardthe possibility of faint OH emission from certain Lbs, based on the sameprocesses as encountered in those sources. We briefly discuss physicalconditions allowing OH emission in the envelope, and the evolutionarystage of objects classified as Lb variables with respect to the AGB.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| H_2_O maser emission from irregular variables.
We have performed a search for the 22 GHz water maser line among 72optically identified irregular and semiregular red variables. Newdetections were made of five stars, while only four of nine objectspreviously known as maser sources were redetected. The probability forthe detection of H_2_O maser emission increases with V light amplitude,and with H-K and K-[12] colours just as in regular Mira and semiregularvariables of SRa- and SRb-types. The detection rate of water masers isabout 25% for nearby Lb objects (D<400 pc) in the sample, comparableto that observed in the SRa and SRb stars. No masers were detected inobjects with mass loss rates <=4x10^-8^Msun_/yr. Maserluminosities are 10^41^-10^43^photons/s similar to that of the bluestMiras and typical SRa and SRb stars showing water maser emission. Acomparison of our data on irregular stars with those previously obtainedon SRa and SRb variables suggests that most radio and infraredproperties are indistinguishable among both classes of objects.
| Oxygen-rich semiregular and irregular variables
All the known oxygen-rich semiregulars and irregulars of spectralclasses K and M with the absolute value of B not greater than 30 deg,Delta(m) not less than 0.5 mag, and, for the semiregulars, periods inthe range of 50 to 400 d are compiled. On the basis of theirdistributions on the sky and their brightnesses in the K band at 2.2microns, it is argued that the semiregulars with a period of 300-400 dappear to belong to the same population as the 'thin disk' Miras in thesame period range and have an exponential scale height from the Galacticplane of about 250 pc. The semiregulars with a period range of 200 to300 d belong to the population of the 'thick disk' Miras with anexponential scale height from the Galactic plane of about 500 pc. On thebasis of the similarities of their space distributions and the presenceof Tc in their atmospheres, and using the pulsational mode calculationsby Ostlie and Cox (1986), it is suggested that the semiregulars with aperiod range of 100-150 d are first and second overtone pulsations ofthe same population of AGB stars as the Miras in their fundamentalpulsational mode with periods longer than 300 d.
| A survey for infrared excesses among high galactic latitude SAO stars
This project involves extending the previous analysis of infraredexcesses among a volume-limited sample of 134 nearby A-K main-sequencestars to a magnitude-limited sample of stars, culled from the SAOCatalog, with excesses determined from the IRAS Point Source Catalogflux density ratios. This new sample includes 5706 B-M type stars, 379of which have infrared excesses. The objective involved use of astatistically complete survey of objects in a standard catalog in orderto assess the frequency with which different physical processes canaffect the infrared output of stars. These processes include, but arenot limited to, orbiting cold particle clouds and the onset of rapidmass loss. It is concluded that cold disks are consistent with theinfrared excesses found among A-G dwarfs and G-K giants in the sample.
| - and Broad-Band Photometry of Red Stars. Northern Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJS...14..307E&db_key=AST
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Observation and Astrometry data
| Constellation: | Virgo |
| Right ascension: | 12h33m08.28s |
| Declination: | +07°15'00.7" |
| Apparent magnitude: | 9.517 |
| Proper motion RA: | -7 |
| Proper motion Dec: | -7.5 |
| B-T magnitude: | 11.211 |
| V-T magnitude: | 9.657 |
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