DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. V. Variables in the Field M31F

We undertook a long term project, DIRECT, to obtain the direct distances to two important galaxies in the cosmological distance ladder -- M31 and M33 -- using detached eclipsing binaries (DEBs) and Cepheids. While rare and difficult to detect, DEBs provide us with the potential to determine these distances with an accuracy better than 5%. The extensive photometry obtained in order to detect DEBs provides us with good light curves for the Cepheid variables. These are essential to the parallel project to derive direct Baade-Wesselink distances to Cepheids in M31 and M33. For both Cepheids and eclipsing binaries, the distance estimates will be free of any intermediate steps. As a first step in the DIRECT project, between September 1996 and October 1997 we obtained 95 full/partial nights on the F. L. Whipple Observatory 1.2 m telescope and 36 full nights on the Michigan-Dartmouth-MIT 1.3 m telescope to search for DEBs and new Cepheids in the M31 and M33 galaxies. In this paper, fifth in the series, we present the catalog of variable stars found in the field M31F [(\alpha,\delta)= (10.\arcdeg10, 40.\arcdeg72), J2000.0]. We have found 64 variable stars: 4 eclipsing binaries, 52 Cepheids and 8 other periodic, possible long period or non-periodic variables. The catalog of variables, as well as their photometry and finding charts, is available via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.Comment: submitted to the Astronomical Journal, 31 pages, 18 figures; paper and data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/DIRECT/ and through WWW at http://cfa-www.harvard.edu/~kstanek/DIRECT

Transitional YSOs: Candidates from Flat-Spectrum IRAS Sources

We are searching for Young Stellar Objects (YSOs) near the boundary between protostars and pre-main sequence objects, what we have termed transitional YSOs. We have identified a sample of 125 objects as candidate transitional YSOs on the basis of IRAS colors and optical appearance on DSS images. We find that the majority of our objects are associated with star-forming regions, confirming our expectation that the bulk of these are YSOs. We present optical, near-IR and high-resolution IRAS images of 92 objects accessible from the northern and 62 from the southern hemisphere. The objects have been classified on the basis of their morphology and spectral index. Of the 125 objects, 28 have a variety of characteristics very similar to other transitional YSOs, while another 22 show some of these characteristics, suggesting that these transitional YSOs are not as rare as predicted by theory.Comment: 4 pages, 3 figures, to appear in proc. 33rd ESLAB Symposium ``Star Formation from the Small to the Large Scale'', eds. F. Favata et al., ESA SP-44

DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. III. Variables in the Field M31C

We undertook a long term project, DIRECT, to obtain the direct distances to two important galaxies in the cosmological distance ladder -- M31 and M33 -- using detached eclipsing binaries (DEBs) and Cepheids. While rare and difficult to detect, DEBs provide us with the potential to determine these distances with an accuracy better than 5%. The extensive photometry obtained in order to detect DEBs provides us with good light curves for the Cepheid variables. These are essential to the parallel project to derive direct Baade-Wesselink distances to Cepheids in M31 and M33. For both Cepheids and eclipsing binaries, the distance estimates will be free of any intermediate steps. As a first step in the DIRECT project, between September 1996 and October 1997 we obtained 95 full/partial nights on the F. L. Whipple Observatory 1.2 m telescope and 36 full nights on the Michigan-Dartmouth-MIT 1.3 m telescope to search for DEBs and new Cepheids in the M31 and M33 galaxies. In this paper, third in the series, we present the catalog of variable stars, most of them newly detected, found in the field M31C [(alpha,delta)=(11.10, 41.42) deg, J2000.0}]. We have found 115 variable stars: 12 eclipsing binaries, 35 Cepheids and 68 other periodic, possible long period or non-periodic variables. The catalog of variables, as well as their photometry and finding charts, is available via anonymous ftp and the World Wide Web. The complete set of the CCD frames is available upon request.Comment: submitted to the Astronomical Journal, 39 pages, 27 figures; paper and data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/DIRECT/ and through WWW at http://cfa-www.harvard.edu/~kstanek/DIRECT

The DIRECT project: Catalogs of stellar objects in nearby galaxies. II. Eastern arm and NGC 206 in M31

DIRECT is a project to directly obtain the distances to two important galaxies in the cosmological distance ladder, M31 and M33, using detached eclipsing binaries and Cepheids. As part of our search for these variables, we have obtained photometry and positions for thousands of stellar objects within the monitored fields, covering an area of 557.8 arcmin^2. In this research note we present the equatorial coordinates and BVI photometry for 26712 stars in the M31 galaxy, along the eastern arm and in the vicinity of the star forming region NGC206.Comment: 2 LaTeX pages, 2 Postscript figures, submitted to Astronomy & Astrophysic

Chandra Studies of the X-ray Point Source Luminosity Functions of M31

Three different M31 disk fields, spanning a range of stellar populations, were observed by Chandra. We report the X-ray point source luminosity function (LF) of each region, and the LF of M31's globular clusters, and compare these with each other and with the LF of the galaxy's bulge. To interpret the results we also consider tracers of the stellar population, such as OB associations and supernova remnants. We find differences in the LFs among the fields, but cannot definitively relate them to the stellar content of the fields. We find that stellar population information, average and maximum source luminosities, X-ray source densities, and slopes of the LF are useful in combination.Comment: 7 pages, 3 figures, accepted for publication in ApJ. Higher-resolution figures available on reques

Identification of 13 Cepheids and 333 Other Variables in M31

We present Cousins $R$ and $I$ band photometry of variable stars in a $\sim13'\times 13'$ region in the disk of M31 galaxy, obtained during 141 nights. Of the 26 Cepheid variables present in the region, two are newly discovered, 11 are classified as Cepheids for the first time and 13 are confirmed as Cepheids. The extensive photometry of these Cepheids enabled us to determine precise phase and amplitude of pulsation which ranges from 0.11 to 0.48 mag in $R$ band. The period of variability ranges from $\sim$7.5 to 56 days. The period-luminosity diagram is used to derive a distance modulus of 24.49$\pm$0.11 mag for M31 galaxy. We also report variability in 333 other stars, of them, 115 stars appear to be long period variables, 2 suspected eclipsing binaries and remaining 216 are irregular variables.Comment: Accepted for publication in A&A, 9 figures, the paper and figures with better resolution can be downloaded from http://cdfinfo.in2p3.fr/Downloads/cosmobs/yogesh/paper

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

We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the KPNO 4-m telescope. The survey covers 2.2 sq degrees of M31, and 0.8 sq degrees of M33, chosen so as to include all of the regions currently active in forming massive stars. The catalog contains 371,781 and 146,622 stars in M31 and M33, respectively, where every star has a counterpart (at least) in B, V, and R. We compare our photometry to previous studies. We provide cross references to the stars confirmed as members by spectroscopy, and compare the location 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. We also present the results of newly obtained spectroscopy, which identifies 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.Comment: Accepted by the Astronomical Journal. A version with higher resolution figures can be found at: http://www.lowell.edu/users/massey/M3133.pdf.g

X-ray Point Sources in The Central Region of M31 as seen by Chandra

We report on \chandra observations of the central region of M31. By combining eight \chandra ACIS-I observations taken between 1999 and 2001, we have identified 204 X-ray sources within the central $\sim 17'\times17'$ region of M31, with a detection limit of $\sim 2\times10^{35}$\lum. Of these 204 sources, 22 are identified with globular clusters, 2 with supernova remnants, 9 with planetary nebula, and 9 as supersoft sources. By comparing individual images, about 50% of the sources are variable on time scales of months. We also found 13 transients, with light curves showing a variety of shapes. We also extracted the energy spectra of the 20 brightest sources; they can be well fit by a single power-law with a mean photon index of 1.8. The spectral shapes of 12 sources are shown to be variable, suggesting that they went through state changes. The luminosity function of all the point sources is consistent with previous observations (a broken power-law with a luminosity break at $1.7\times10^{37}$\lum). However, when the X-ray sources in different regions are considered separately, different luminosity functions are obtained. This indicates that the star-formation history might be different in different regions.Comment: 42 pages, 9 figures, ApJ, accepted, Higher-resolution figures available on reques

The Discovery of a Spatially-Resolved Supernova Remnant in M31 with Chandra

Chandra observations of M31 allow the first spatially resolved X-ray image of a supernova remnant (SNR) in an external spiral galaxy. CXOM31 J004327.7+411829 is a slightly elongated ring-shaped object with a diameter of ~11'' (42 pc). In addition, the X-ray image hints that the chemical composition of the SNR is spatial dependent. The X-ray spectrum of the SNR can be well fitted with a Raymond-Smith model or a non-equilibrium ionization model. Depending on the spectral model, the 0.3-7 keV luminosity is between 3.2x10^36 erg/s and 4.5x10^37 erg/s. The age of the SNR is estimated to be 3210-22300 years and the number density of ambient gas is ~0.003-0.3 cm^-3. This suggests that the local interstellar medium around the SNR is low.Comment: 5 pages, 3 figures; accepted for publication in ApJ