The mass of the black hole in GRS 1915+105: new constraints from IR spectroscopy

GRS 1915+105 has the largest mass function of any Galactic black hole system, although the error is relatively large. Here we present spectroscopic analysis of medium-resolution IR VLT archival data of GRS 1915+105 in the K-band. We find an updated ephemeris, and report on attempts to improve the mass function by a refinement of the radial velocity estimate. We show that the spectra are significantly affected by the presence of phase-dependent CO bandhead emission, possibly originating from the accretion disc: we discuss the impact this has on efforts to better constrain the black hole mass. We report on a possible way to measure the radial velocity utilising apparent H-band atomic absorption features and also discuss the general uncertainty of the system parameters of this well-studied objectComment: 7 pages, 7 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Addendum: "The Dynamics of M15: Observations of the Velocity Dispersion Profile and Fokker-Planck Models" (ApJ, 481, 267 [1997])

It has recently come to our attention that there are axis scale errors in three of the figures of Dull et al. (1997, hereafter D97). D97 presented Fokker-Planck models for the collapsed-core globular cluster M15 that include a dense, centrally concentrated population of neutron stars and massive white dwarfs, but do not include a central black hole. In this Addendum, we present corrected versions of Figures 9, 10, and 12, and an expanded version of Figure 6. This latter figure, which shows the full run of the velocity dispersion profile, indicates that the D97 model predictions are in good agreement with the moderately rising HST-STIS velocity dispersion profile for M15 reported by Gerssen et al. (2002, astro-ph/0209315). Thus, a central black hole is not required to fit the new STIS velocity measurements, provided that there is a sufficient population of neutron stars and massive white dwarfs. This conclusion is consistent with the findings of Gerssen et al. (2002, astro-ph/0210158), based on a reapplication of their Jeans equation analysis using the corrected mass-to-light profile (Figure 12) for the D97 models.Comment: 4 pages, 4 figures, submitted to Ap

The light curve of the companion to PSR B1957+20

We present a new analysis of the light curve for the secondary star in the eclipsing binary millisecond pulsar system PSR B1957+20. Combining previous data and new data points at minimum from the Hubble Space Telescope, we have 100% coverage in the R-band. We also have a number of new K_s-band data points, which we use to constrain the infrared magnitude of the system. We model this with the Eclipsing Light Curve code (ELC). From the modelling with the ELC code we obtain colour information about the secondary at minimum light in BVRI and K. For our best fit model we are able to constrain the system inclination to 65 +/- 2 degrees for pulsar masses ranging from 1.3 -- 1.9 M_sun. The pulsar mass is unconstrained. We also find that the secondary star is not filling its Roche lobe. The temperature of the un-irradiated side of the companion is in agreement with previous estimates and we find that the observed temperature gradient across the secondary star is physically sustainable.Comment: 6 pages, 4 figures & 3tables. Accepted for publication in MNRA