A Survey of Local Group Galaxies Currently Forming Stars. III. A Search for Luminous Blue Variables and Other Hα Emission-Line Stars

By Philip Massey, R. McNeill, Kirsty Olsen, P. Hodge, C. Blaha, George Jacoby, R. C. Smith, Shay Strong. 2007

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We describe a search for Hα emission-line stars in M31, M33, and seven dwarfs in or near the Local Group (IC 10, NGC 6822, WLM, Sextans B, Sextans A, Pegasus, and the Phoenix dwarf) using interference filter imaging with the KPNO and CTIO 4 m telescopes and Mosaic cameras. The survey is aimed primarily at identifying new luminous blue variables (LBVs) from their spectroscopic similarity to known LBVs, avoiding the bias toward photometric variability, which may require centuries to manifest itself if LBVs go through long quiescent periods. Follow-up spectroscopy with WIYN confirms that our survey detected a wealth of stars whose spectra are similar to the known LBVs. We "classify" the spectra of known LBVs and compare these to the spectra of the new LBV candidates. We demonstrate spectacular spectral variability for several of the new LBV candidates, such as AM2, previously classified as a Wolf-Rayet star (WR), which now shows Fe I, Fe II, and Balmer emission lines but neither the N III λλ4634, 4642 nor the He II λ4686 emission it did in 1982. Profound spectral changes are also noted for other suspected and known LBVs. Several of the LBV candidates also show >0.5 mag changes in V over the past 10-20 years. The number of known or suspected LBVs is now 24 in M31, 37 in M33, 1 in NGC 6822, and 3 in IC 10. We estimate that the total number of LBVs in M31 and M33 may be several hundred, in contrast to the eight known historically through large-scale photometric variability. This has significant implications for the timescale of the LBV phase. We also identify a few new WRs and peculiar emission-line objects.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/205869901ecedc0070734121a2f4f0029c106397

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Citations in the corpus

Luminous blue variables are antisocial: their isolation implies that they are kicked mass gainers in binary evolution (2014, background): “Massey et al. (2007) find an order of magnitude more LBV candidates than bona fide LBVs in nearby galaxies, and massive dusty shells around massive stars in the MW suggest a similarly large number here (Wachter et al. 2010; Gvaramadze et al. 2010).”
Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars (2014, background): “Examining populations in nearby galaxies, Massey et al. (2007) find that there are more than an order of magnitude more spectroscopically similar LBV candidates than there are LBVs confirmed by their variability.”
A NEW CLASS OF LUMINOUS TRANSIENTS AND A FIRST CENSUS OF THEIR MASSIVE STELLAR PROGENITORS (2008, background): “…magnitude ofMB ≈ −19.2, a distance of≈ 0.96 Mpc (distance modulusµ = 24.92; Bonanos et al. 2006), and it has extensive optical (e.g., Hartman et al. 2006; Massey et al. 2006, hereafter M06), Hα (Massey et al. 2007, hereafter M07), and MIR and FIR imaging (McQuinn et al. 2007, here- after Mc07).”
ON THE MAXIMUM MASS OF STELLAR BLACK HOLES (2009, background): “It 1 2 is interesting to note that the star formation rate in dwarf galaxy IC10 is very high, and its metallicity is low ∼ 0.3Z⊙ (Massey et al. 2007).”