A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33

By Philip Massey, Kirsty Olsen, P. Hodge, Shay Strong, George Jacoby, W. Schlingman, R. C. Smith. 2006

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We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the Kitt Peak National Observatory 4 m telescope. We describe our data reduction and automated photometry techniques in some detail, as we will shortly perform a similar analysis of other Local Group galaxies. The present study covered 2.2 deg2 along the major axis of M31 and 0.8 deg2 on M33, chosen so as to include all of the regions currently active in forming massive stars. We calibrated our data using photometry from the Lowell 1.1 m telescope, and this external method resulted in millimagnitude differences in the photometry of overlapping fields, providing some assurance that our photometry is reliable. The final catalog contains 371,781 and 146,622 stars in M31 and M33, respectively, where every star has a counterpart in (at least) the B, V, and R passbands. Our survey goes deep enough to achieve 1%-2% photometry at 21 mag (corresponding to stars more massive than 20 M⊙) and achieves <10% errors at U ∼ B ∼ V ∼ R ∼ I ∼ 23 mag. Although our typical seeing was only modest (0.″8-1.″4, with median 1.″0) by some standards, we find excellent correspondence between our catalog sources and those we see in our Hubble Space Telescope ACS data for OB48, a crowded region in M31. We compare our final photometry with that of others and find good agreement with the CCD catalog of M31 stars by Magnier et al., although our study covers twice the area and goes about 2 mag deeper. There is also excellent agreement with the CCD "DIRECT" surveys of M31 and M33. The photographic studies of others fare less well, particularly at the faint end in V, where accurate background subtraction is needed for good photometry. We provide cross-references to the stars confirmed as members by spectroscopy and compare the locations of these to the complete set in color-magnitude diagrams. While follow-up spectroscopy is needed for many projects, we demonstrate the success of our photometry in being able to distinguish M31/M33 members from foreground Galactic stars. Finally, we present the results of a single night of spectroscopy on the WIYN 3.5 m telescope, examining the brightest likely members of M31. The spectra identify 34 newly confirmed members, including B-A supergiants, the earliest O star known in M31, and two new luminous blue variable candidates whose spectra are similar to that of P Cygni.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

THE EMISSION BY DUST AND STARS OF NEARBY GALAXIES IN THE HERSCHEL KINGFISH SURVEY (2011, methodology): “For NGC 598, we obtained Hα data from Massey et al. (2006), from which we measured a flux density of 2.4 ± 0.2 × 10−10 erg cm−2 s−1, which is slightly lower (by 0.15 dex) than the value given by Kennicutt et al. For NGC 2146, which was in neither sample, we use the Hα flux measured by Marcum et al.…”
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).”
A Survey of Local Group Galaxies Currently Forming Stars. III. A Search for Luminous Blue Variables and Other Hα Emission-Line Stars (2007, methodology): “Their fields do not cover all of M31 and M33, so the lack of designation of a variable is not particularly telling, but several of these stars are listed.”
THE YELLOW SUPERGIANT PROGENITOR OF THE TYPE II SUPERNOVA 2011dh IN M51 (2011, result): “We compared the U − B and V − I colors of the progenitor candidate to those of the observed population of Wolf-Rayet (WR) stars in M31 (Massey et al. 2006).”
THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY. X. ULTRAVIOLET TO INFRARED PHOTOMETRY OF 117 MILLION EQUIDISTANT STARS (2014, methodology): “This catalog has been superseded by Massey et al. (2006), which contains a similar number of stars in 5 bands with improved photometric and astrometric precision and which has led to a census of the brightest and most massive M31 members.”