Variable Stars In M31 Research Articles

Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

Abstract We present HR diagrams for the massive star populations in M31 and M33, including several different types of emission-line stars: the confirmed luminous blue variables (LBVs), candidate LBVs, B[e] supergiants, and the warm hypergiants. We estimate their apparent temperatures and luminosities for comparison with their respective massive star populations and evaluate the possible relationships of these different classes of evolved, massive stars, and their evolutionary state. Several of the LBV candidates lie near the LBV/S Dor instability strip that supports their classification. Most of the B[e] supergiants, however, are less luminous than the LBVs. Many are very dusty with the infrared flux contributing one-third or more to their total flux. They are also relatively isolated from other luminous OB stars. Overall, their spatial distribution suggests a more evolved state. Some may be post-RSGs (red supergiants) like the warm hypergiants, and there may be more than one path to becoming a B[e] star. There are sufficient differences in the spectra, luminosities, spatial distribution, and the presence or lack of dust between the LBVs and B[e] supergiants to conclude that one group does not evolve into the other.

Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidate LBVs, B[e] Supergiants, and the Warm Hypergiants: How to Tell Them Apart*

Abstract In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe ii emission line stars, the B[e] supergiants, and the warm hypergiants. Many of these objects are spectroscopically similar and are often confused with each other. We examine their similarities and differences and propose the following guidelines that can be used to help distinguish these stars in future work. (1) The B[e] supergiants have emission lines of [O i] and [Fe ii] in their spectra. Most of the spectroscopically confirmed sgB[e] stars also have warm circumstellar dust in their spectral energy distributions (SEDs). (2) Confirmed LBVs do not have the [O i] emission lines in their spectra. Some LBVs have [Fe ii] emission lines, but not all. Their SEDs show free–free emission in the near-infrared but no evidence for warm dust. Their most important and defining characteristic is the S Dor-type variability. (3) The warm hypergiants spectroscopically resemble the LBVs in their dense wind state and the B[e] supergiants. However, they are very dusty. Some have [Fe ii] and [O i] emission in their spectra like the sgB[e] stars, but are distinguished by their A- and F-type absorption-line spectra. In contrast, the B[e] supergiant spectra have strong continua and few if any apparent absorption lines. Candidate LBVs should share the spectral characteristics of the confirmed LBVs with low outflow velocities and the lack of warm circumstellar dust.

Variable stars in M31 from the MEGA survey

AbstractThe MEGA microlensing survey is introduced and several topics about variable stars in M31 are discussed. An adopted model population of semiregular (SR) variable stars is presented, and the efficiency to recover these stars in M31 in a specific example MEGA dataset is predicted. The period-flux amplitude relation of the SRs discovered by MEGA could be used to measure the inclination of the M31 disk.

Luminous variable stars in M31 and M33

view Abstract Citations (37) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Luminous variable stars in M31 and M33. Humphreys, R. M. Abstract Spectra and UBVRI photometry of four luminous blue variables in M31 and four luminous blue variables in M33 are presented along with a spectrum of a red supergiant variable in M31 and a 2-micron measurement of one of the blue variables in M31. The spectra were obtained over the wavelength range from about 3000 to 5500 A at a dispersion of 79 A/mm with a resolution of approximately 4 A. The spectra of two blue variables in M31 and one in M33 are found to be characterized by Fe II and forbidden Fe II emission lines, hydrogen and helium emission, a very strong UV continuum, and no evident Balmer discontinuity. Changes in the spectra of two other blue variables in M33 are briefly described, and the spectra of all eight blue variables are shown to be very similar. It is concluded that the eight blue variables in M31 and M33, together with Eta Car in the Milky Way, S Dor in the Large Magellanic Cloud, and related objects in the latter two galaxies, form a recognizable group of very luminous hot stars with very low surface gravities. Publication: The Astrophysical Journal Pub Date: January 1978 DOI: 10.1086/155797 Bibcode: 1978ApJ...219..445H Keywords: Andromeda Galaxy; Stellar Luminosity; Stellar Spectrophotometry; Supergiant Stars; Ubv Spectra; Variable Stars; Absorption Spectra; Emission Spectra; Hot Stars; Infrared Spectra; Stellar Magnitude; Astrophysics; Andromeda Nebula:Blue Variables; Blue Variables:Galaxies; Galaxies:Supergiants full text sources ADS | data products SIMBAD (20) NED (3) GCPD (1)