We have used Hubble Space Telescope to obtain moderate resolution 11505700 Å spectroscopy of the nucleus of M33 and a blue star ∼ 1 arcsec NNW of the nucleus in an attempt to find the optical counterpart of the nuclear X-ray source and to characterize stellar populations in the nuclear region. The STIS spectra of the nucleus can be modelled in terms of two starbursts, one with a mass of about 9...

We identify red supergiants (RSGs) in our spiral neighbors M31 and M33 using near-IR (NIR) photometry complete to a luminosity limit of log L/Lo=4.0. Our archival survey data cover 5 deg^2 M31, 3 for M33, are likely spatially these massive stars. Gaia is used remove foreground stars, after which the RSGs can be separated from asymptotic giant branch (AGB) stars color-magnitude diagram. The deri...

In prior work, Chandra and Gemini-North observations of the eclipsing X-ray binary M33 X-7 have yielded measurements of the mass of its black hole primary and the system’s orbital inclination angle of unprecedented accuracy. Likewise, the distance to the binary is known to a few percent. In an analysis based on these precise results, fifteen Chandra and XMM-Newton X-ray spectra, and our fully r...

We present resolved stellar photometry of 4 fields along the major axis of the M33 disk from images taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope. The photometry provides a detailed census of the red clump in all fields and reaches the ancient main sequence in the outermost field. Through detailed modeling of the color-magnitude diagrams, we find that the percenta...

We present the results of deep I and V-band photometry of the halo stars near the southeast minor axis of the Local Group spiral galaxy M33. An (I, V − I) color-magnitude diagram distinctly reveals the red giant branch stars at the bright end of the color-magnitude diagram. A luminosity function in the I-band which utilizes a background field to remove the contaminating effects of Galactic fore...