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Publications and source records attributed to Garcia, Michael R..
The goal of this program is to study black holes, both in our Galaxy and in nearby galaxies. We aim to study both "stellar mass" x-ray binaries containing black holes (both in our Galaxy and in nearby galaxies), and super-massive black holes in nearby galaxies.
We present optical photometry and spectroscopy and Burst and Transient Source Experiment (BATSE) observations of the X-ray nova GRO J0422+32, obtained during outburst and its subsequent decay to quiescence. Although the X-ray and optical properties of GRO J0422+32 are broadly similar to those of other X-ray novae, it is unique in several respects. The unusually protracted decay to quiescence of the optical light curve has been punctuated by at least two minioutbursts of approximately 4 mag. The BATSE and optical outbursts are each separated by approximately 120 days. We find that the optical luminosity of GRO J0422+32 during the primary outburst is dominated by reprocessing of E greater than 10 keV X-rays. In contrast, the optical minioutbursts are most likely generated by an intrinsically bright disk rather than X-ray reprocessing: they do not appear to have any X-ray counterparts. Extremely broad (up to 6000 km/s FWZI) absorption lines have also been observed during both primary outbursts and minioutbursts. During the second minioutburst, H-alpha and H-beta emission was observed superposed on redshifted absorption features. We find that the interoutburst light curve of GRO J0422+32 may be inconsistent with an accretion disk instability as the origin of the minioutbursts. Finally, a transient 5.1/10.2 hr modulation, which may be related to the orbital period, has been observed during roughly half of our observations. However, confirmation of the orbital period must await observations in quiescence.
We present an analysis of new and archival photometric and spectroscopic observations of the symbiotic star AG Draconis. This binary has undergone several 1 - 3 mag optical and ultraviolet eruptions during the past 15 years. Our combination of optical and ultraviolet spectroscopic data allow a more complete analysis of this system than in previous papers. AG Dra is composed of a K-type bright giant M(sub g) approximately 1.5 solar mass) and a hot, compact star M(sub h approximatelly 0.4 - 0.6 solar mass) embedded in a dense, low metallicity nebula. The hot component undergoes occasional thermonuclear runaways that produce 2 - 3 mag optical/ultraviolet eruptions. During these eruptions, the hot component develops a low velocity wind that quenches x-ray emission from the underlying hot white dwarf. The photoionized nebula changes its volume by a factor of 5 throughout an eruptin cycle. The K bright giant occults low ionization emission lines during superior conjunctions at all outburst phases but does not occult high ionization lines in outburst (and perhaps quiescence). This geometry and the component masses suggest a system inclination of i approximately 30 deg - 45 deg.
Observations with the ROSAT HRI allow detection of weak X-ray flux from the low-mass X-ray binary (LMXB) 4U 2129+47 during its current quiescent state. The quiescent luminosity is similar to that seen in several other quiescent LMXBs containing neutron stars. The quiescent X-ray light curve may not show the eclipse seen when the source was in its high state, which would indicate that the enhanced vertical structure present in the disk during the high state has collapsed. This in turn provides support for the idea that the vertical structure in LMXB accretion disks is a consequence of high X-ray luminosity. A comparison of the absorption of low-energy X-rays due to the interstellar medium (determined from Einstein IPC observations) and the optical extinction does not rule out the triple system hypothesis.
It is shown that earlier estimates of the number of cataclysmic variables (CVs) to be expected from tidal capture in globular clusters may have been considerably too high, since many such binaries will result in unstable mass transfer, and thus not become CVs after all. In particular, CVs with white dwarf masses less than or obout 1.0 solar mass will be supressed. Such unstable mass transfer events may produce some of the cluster mass loss required to stabilize the cluster core. The smaller number of stable CVs predicted may suggest a reconsideration of the nature of some of the low-luminosity cluster X-ray sources.
MMT observations of AC 211, the optical counterpart of the high-luminosity X-ray source in globular cluster M15, are presented. The observation of Naylor et al. (1988) that the He I absorption is blueshifted by more than 100 km/s with respect to the mean velocity of the cluster is confirmed. It is shown that if the absorption occurs in a stream of gas outflowing from the L2 point of a binary system, as might be expected for a common envelope binary, both the blueshift and the unexpectedly low velocity variations of the He I lines can be understood. The model predicts that the He I velocity curve is not sinusoidal.
Surprising observations of radial velocity variations and spectral type of the low-mass X-ray binary (LMXRB) 4U 2129 + 47 made from June 1987 to October 1988 are reported. Shifts in the mean radial velocity, the lack of variations in the orbital period, and the anomalous spectral type suggest that this system is a hierarchical triple with an inner boundary consisting of an LMXRB with a 5.24 hr period and an F7 V star in a much larger orbit around the inner binary. A necessary consequence of such a triple would be a cycle of about 45 yr in the mean eccentricity of the inner binary, which is consistent with the pattern of on and off states that have been observed since the 1930s.
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Einstein MPC observations of the 5.2-h binary 4U 2129 + 47 are analyzed, and a type 1 X-ray burst with rise time 6.5 + or 1.5 s, peak 2-10-keV flux about 1 nerg/sq cm s, and peak color temperature 2.8 + 0.9 or - 0.7 keV is detected in data for 22:01:03 UT on December 15, 1978. It is inferred that the compact component of the binary is a neutron star, and anomalies in the burst (e.g., peak luminosity 500 times lower than the Eddington limit) are interpreted in terms of the accretion-disk-corona (ADC) model of McClintock et al. (1982). Assuming that the burst itself is normal, an ADC with temperature about 10 to the 8th K, radius 4 x 10 to the 10th cm, and electron-scattering optical depth about 2.5 is predicted, making this object the first neutron star with a mass (0.6 + or - 0.2 solar mass according to Horne et al., 1986) well below the Chandrasekhar limit.