The weak X-ray transient XTE J1739-302, characterized by extremely short outbursts, has recently been identified with a reddened star. Here we present spectroscopy and photometry of the counterpart, identifying it as a O8 Iab(f) supergiant at a distance of ~2.3 kpc. XTE J1739-302 thus becomes the prototype of the new class of supergiant fast X-ray transients (SFXTs). The optical and infrared spectra of the counterpart to XTE J1739-302 do not reveal any obvious characteristics setting it apart from other X-ray binaries with supergiant companions, which display a very different type of X-ray light curve.

Recent Chandra X-Ray Observatory observations have revealed a large population of faint X-ray point sources in the Galactic center. The observed population consists of ≳2000 faint sources in the luminosity range ~1031-1033 ergs s-1. The majority of these sources (70%) are described by hard spectra, while the rest are rather soft. The nature of these sources still remains unknown. Belczynski & Taam demonstrated that X-ray binaries with neutron star or black hole accretors may account for most of the soft sources, but are not numerous enough to account for the observed number and X-ray properties of the faint hard sources. A population synthesis calculation of the Galactic center region has been carried out. Our results indicate that the numbers and X-ray luminosities of intermediate Polars are consistent with the observed faint hard Galactic center population.

We report on an unprecedented infrared time series of spectra of V1187 Sco, a very fast ONeMg nova. The observations covered a 56 day period (2004 August 6-September 30) starting 2 days after the nova's peak brightness. Time evolution of the spectra revealed changing line strengths and profiles on timescales of less than a day to weeks as the nova evolved from early postmaximum to early coronal phases. When our ground-based optical and Spitzer Space Telescope data were combined, the wavelength coverage of 0.38-36 μm allowed an accurate spectral energy distribution to be derived when it was about 6 weeks after outburst. Developing double structure in the He I lines showed them changing from narrow to broad in only a few days. Using the O I lines in combination with the optical spectra, we derived a reddening of E(B - V) = 1.56 ± 0.08 and a distance of 4.9 ± 0.5 kpc. Modeling of the ejected material strongly suggested that it was geometrically thick with ΔR/R = 0.8-0.9 (more of a wind than a shell) and a low filling factor of order a few percent. The line shapes were consistent with a cylindrical jet, bipolar, or spherical Hubble flow expansion with a maximum speed of about -3000 km s-1. The central peak appeared to be more associated with the spherical component, while the two peaks (especially in Hβ) suggested a ring with either a lower velocity component or with its axis inclined to the line of sight.

XTE J1739-302 is a transient X-ray source with unusually short outbursts, lasting on the order of hours. Here we give a summary of X-ray observations we have made of this object in outburst with the Rossi X-Ray Timing Explorer (RXTE) and at a low level of activity with the Chandra X-Ray Observatory, as well as observations made by other groups. Visible and infrared spectroscopy of the mass donor of XTE J1739-302 are presented in a companion paper. The X-ray spectrum is hard both at low levels and in outburst, but somewhat variable, and there is strong variability in the absorption column from one outburst to another. Although no pulsation has been observed, the outburst data from multiple observatories show a characteristic timescale for variability on the order of 1500 - 2000 s. The Chandra localization (R: A: 17(h)39(m)11(s): s 58, decl. = 30 degrees 20'37"6, J2000.0) shows that despite being located less than 2 degrees from the Galactic center and highly absorbed, XTE J1739 similar to 302 is actually a foreground object with a bright optical counterpart. The combination of a very short outburst timescale and a supergiant companion is shared with several other recently discovered systems, forming a class we designate as supergiant fast X-ray transients (SFXTs). Three persistently bright X-ray binaries with similar supergiant companions have also produced extremely short, bright outbursts: Cyg X-1, Vela X-1, and 1E 1145.1-6141.

We present phase-resolved low-resolution JHK and higher resolution K-band spectroscopy of the polar VV Pup. All observations were obtained when VV Pup was in a low-accretion state having a K magnitude near 15. The low-resolution observations reveal cyclotron emission in the J band during some phases, consistent with an origin near the active 30.5 MG pole on the white dwarf. The secondary in VV Pup appears to be a normal M7 V star, and we find that the H- and K-band fluxes are entirely due to this star at all orbital phases during the low-accretion state. We use our higher resolution Keck spectroscopy to produce the first K-band radial velocity curve for VV Pup. Our orbital solution yields K-2 = 414 +/- 27 km s(-1) and leads to mass estimates of M-1 = 0.73 +/- 0.05 M-circle dot and M-2 = 0.10 +/- 0.02 M-circle dot. We find that the mass accretion rates during the normal low states of the polars VV Pup, EF Eri, and EQ Cet are near 10(-13) M-circle dot yr(-1). The fact that M is not zero in low-state polars indicates active secondary stars in these binary systems, including the substellar donor star present in EF Eri.

We present two epochs of low-state, near-IR spectroscopy of the polar prototype AM Her, along with K-band spectroscopy and JHK photometry. Combining our data with long-term (RoboScope) photometry of the system, we determine a new spectroscopic ephemeris for AM Her. According to the new ephemeris, the primary photometric minimum of the high-state light curve of the system is centered at phase zero. Our K-band spectrum, in which the Brγ and He I (2.06 μm) lines are essentially absent, confirms that during the low state, accretion was negligible. Ellipsoidal variations dominate the J-band light curve, whereas cyclotron harmonics are prominent in the H- and K-band light curves. Cyclotron emission during a time of negligible accretion has been observed in other low- polars. The Hα line is often triple peaked, and all three components follow the motion of the secondary star. The central peak likely originates from the irradiated inner hemisphere of the secondary. The blue/red satellite components reach velocities of ∼300 km s-1 with respect to the secondary and coincide in phase with flaring events recently discovered from a photometric campaign. We argue that the satellite behavior is consistent with motions in large loop coronal structures on the secondary star.

We present K-band spectra for 12 cataclysmic variables (CVs) with orbital periods under 6 hr. We confidently detect the secondary stars in nine of these systems and may have detected them in the other three. Nine of the 12 CVs clearly have CO first-overtone absorption features that are weaker than they should be for the derived spectral type. We demonstrate that, in general, the weak CO features are due to a carbon deficiency in the secondary star. In the case of U Gem, UU Aql, and TW Vir the carbon abundance in the secondary star appears to be very low, likely only a few percent of the solar value. Deficits of carbon, when combined with the detection of 13CO and the ultraviolet detections of enhanced levels of nitrogen in other CV systems, imply that material that has been processed through the CNO cycle is finding its way into the photospheres of CV secondary stars. While several plausible models exist to explain unusual levels of CNO species in CV secondary stars, they do not detail how such species as aluminum, magnesium, or silicon (elements that show abundance anomalies in our spectra) will behave. It appears that the standard model for the formation and evolution of CVs needs substantial revision.

We have used NIRSPEC on Keck II to obtain K-band spectroscopy of several magnetic cataclysmic variables. These data reveal that the secondary stars in these binary systems have spectra that are consistent with normal, late-type dwarfs in both their atomic and molecular line strengths, as well as in the slopes of their continua. This result is in stark contrast to the infrared spectra of their nonmagnetic cousins, nearly all of which show peculiar abundances, especially of CNO species and their isotopes. It appears that the evolutionary path taken by the secondary stars in magnetic systems differs from that for the nonmagnetic systems. We discuss the implications of this result.

The emission from low-mass X-ray binaries (LMXBs) arises from the accretion of mass onto a neutron star or black hole. A knowledge of the amount of mass being accreted as well as changes in this value are therefore essential inputs into models of these systems. Despite the need for this information, we currently lack an easily applied method that allows the accretion rate to be measured. X-ray color-color plots and UV observations can be used for this purpose, but these methods require access to oversubscribed satellites. Even if time is granted on these facilities, there is no guarantee that the source will be in a desired state when the observations take place. In this paper we show that an estimate of the ratio of the mass accretion rate to the Eddington rate can be obtained for Sco X-1 by using the Johnson B magnitude. Based on correlated X-ray and ground-based observations, we find that for Sco X-1, Ṁ/ṀE = -(0.123 ± 0.007)B + 2.543 ± 0.085. This relation is valid when the system is on its normal and lower flaring branches. Based on theoretical models, we suggest that similar relations should also exist for other LMXBs.

Time-resolved IR spectroscopy of WZ Sge was obtained using NIRSPEC on Keck II. We detect CO and H2 emission from the accretion disk, placing WZ Sge in a rarefied class of astronomical objects including young stellar objects and high-luminosity early-type stars. During the eclipse phase, the molecular emission greatly weakens, but no firm evidence for the secondary star is seen, allowing new limits on its luminosity to be determined. The detection of molecular emission provides physical properties T = 3000 K and nH > 1010 cm-3 within the outer disk. Such a cool, dense region not associated with areas of H I and He I emission provides the first observational confirmation of predictions made by accretion disk models.

We present moderate-resolution (R > 1800) infrared K-band spectra of 12 long-period (Porb > 6 hr) cataclysmic variables (CVs). We detect absorption lines from the photospheres of the secondary stars in every system, even though two of them were undergoing outbursts. We have attempted to assign a spectral type to each of the secondary stars, and these classifications are generally consistent with previous determinations. We find evidence for abundance anomalies that include enhancements and/or deficits for all of the species commonly found in K-band spectra of G- and K-type dwarfs. There is, however, only one common abundance anomaly: extremely weak CO features. Only two of the 12 objects appeared to have normal levels of CO absorption. We interpret this as evidence of low carbon abundances. In addition, we detect 13CO absorption in four of the 12 objects. Depleted levels of 12C and enhanced levels of 13C indicate that material that has been processed in the CNO cycle is finding its way into the photospheres of CV secondary stars. In systems with luminous accretion disks, we find that the spectrum of the secondary star is contaminated by a source that flattens (reddens) the continuum. While free-free or classical accretion disk spectra are flatter than the blackbody-like spectra of G and K dwarfs, removal of such contamination from the K-band data results in spectra in which the absorption features become too strong to be consistent with those of G and K dwarfs.

Newly determined high-precision relative proper motions determined from the Hubble Space Telescope Wide Field Planetary Camera 2 are used along with radial velocity measurements to determine the dynamical distance to the globular cluster M15. A comparison of the proper motion and radial velocity dispersions from a sample of 237 stars, located at an average radial distance of about 10'' from the cluster center, yields a cluster distance of 9.98 ± 0.47 kpc. This distance agrees to within the stated errors to other distance estimates but places this object about 5% closer than the currently adopted value of 10.4 kpc. Using this new distance, we estimate that RR Lyrae stars having [Fe/H] = -2.15 have a value of Mv(RR) = 0.51 ± 0.11. We also estimate that M15 has an age of about 13.2 Gyr, which places it among the oldest of the Galactic globular clusters. From a comparison of the observed velocity dispersion with results from recent N-body calculations, we derive a total cluster mass for M15 of MC = 4.5 × 105 M☉.

We present optical and/or infrared photometry of the Type Ia supernovae SN 1991T, SN 1991bg, SN 1999ek, SN 2001bt, SN 2001cn, SN 2001cz, and SN 2002bo. All but one of these supernovae have decline rate parameters, Deltam(15)(B), close to the median value of 1.1 for the whole class of Type Ia supernovae. The addition of these supernovae to the relationship between the near-infrared absolute magnitudes and Deltam(15)(B) strengthens the previous relationships we have found in that the maximum light absolute magnitudes are essentially independent of the decline rate parameter. (SN 1991bg, the prototype of the subclass of fast-declining Type Ia supernovae, is a special case.) The dispersion in the Hubble diagram in JHK is only similar to0.15 mag. The near-infrared properties of Type Ia supernovae continue to be excellent measures of the luminosity distances to the supernova host galaxies because of the need for only small corrections from the epoch of observation to maximum light, low dispersion in absolute magnitudes at maximum light, and the minimal reddening effects in the near-infrared.

We present new phase-resolved H- and K-band spectroscopy of the ultrashort-period magnetic cataclysmic variable EF Eri in its current prolonged "low" state obtained using NIRI on Gemini North and NIRSPEC on Keck II. These new data show that the H-band spectrum of EF Eri appears to be dominated by cyclotron emission during the entire orbital cycle. The K-band spectrum of EF Eri is likewise dominated by cyclotron emission during most of an orbital period, but near binary phase 0.0 the secondary star spectrum may be visible. The lack of strong CO or CH4 absorption features and the weakness of the water vapor features in this spectrum, however, suggests the possibility of peculiar abundances for carbon and/or oxygen. We have used the PHOENIX stellar atmosphere code to produce model brown dwarf spectra with nonsolar abundances of carbon, nitrogen, and oxygen, and achieved limited success in fitting the observed spectra. We conclude that strong, highly variable cyclotron emission is responsible for the photometric variation previously reported for EF Eri. The nature of this cyclotron emission is complex: the H-band spectra show that the dominant cyclotron harmonic at phase 0.5 peaks at 1.65 μm, but at phase 0.0 the harmonic peaks near 1.72 μm. At phase 0.5, there is another cyclotron feature present that peaks in between the H and K bands (near 1.93 μm), but at phase 0.0 no such feature is present. These data suggest that cyclotron emission from both poles is occurring. In the high state, the cyclotron emission has been modeled as coming from the pole that is oriented toward the secondary star. One interpretation for the phase 0.5 cyclotron emission is that it originates from the opposite pole. In its current ultralow state, EF Eri reveals no outward signs of accretion (such as H I emission) but continues to have a few, strong cyclotron features. Thus, EF Eri joins the small group of magnetic cataclysmic variables whose accretion rate is so low that they are in the "bombardment scenario" regime.

Using the Hubble space Telescope Fine Guidance Sensor, we have measured the trigonometric parallax of the bright cataclysmic variable 1223 Sgr. The absolute parallax is πabs = 1.96 ± 0.18 mas, making V1223 Sgr the most distant CV with a well-determined trigonometric parallax. This distance, a Lutz-Kelker correction, and the previously measured extinction yield an absolute visual high-state magnitude MV = 4.0 ± 0.2. We outline a model, which is consistent with the observed spin-down of the white dwarf and provides for much of the UV/optical emission by reverberation of X-rays. From previous X-ray and UV/optical data, we derive an accretion luminosity Lacc = (2.6 ± 0.8) × 10 34 erg s −1 , a white dwarf mass M1 = 0.93 ± 0.12 M� , and an accretion rate u M = (1.4 ± 0.3) × 10 17 gs −1 ,

We present new, high-precision astrometric parallaxes for three cataclysmic variables: WZ Saggitae, YZ Cancri, and RU Pegasi, obtained using the Fine Guidance Sensors on the Hubble Space Telescope. The addition of these three parallaxes to the existing data set allows us to examine the outburst luminosities for dwarf novae spanning the orbital period range 1.36 hr less than or equal to P-orb less than or equal to 8.99 hr. We find that, after correcting for the orbital inclination, there is a simple linear relationship between the absolute visual magnitude at outburst and the orbital period. Such a relationship suggests that the only difference in the outbursts between long- and short-period systems is the actual physical size of their accretion disks. When we compare the rare outbursts of three intermediate polar systems (EX Hydrae, TV Columbae, and V1223 Sagittarii), and the visual high states of the nova-like variable RW Tri, four other cataclysmic variables with published HST parallaxes, with the new M-V-P-orb relationship derived for the dwarf novae, we find that the absolute visual magnitudes during the "outbursts'' of these four systems attain the luminosity predicted for their orbital period. This suggests that these short-lived outbursts may also be steady state accretion events like the eruptions of dwarf novae.

We report the detection of the lowest mass extrasolar planet yet found around a Sun-like star-a planet with an M sin i of only 14.21+/-2.91 M-circle plus in an extremely short period orbit (P=2.808 days) around rho(1) Cancri, a planetary system that already has three known planets. Velocities taken from late 2003-2004 at McDonald Observatory with the Hobby-Eberly Telescope revealed this inner planet at 0.04 AU. We estimate an inclination of the outer planet rho(1) Cancri d, based on Hubble Space Telescope Fine Guidance Sensor measurements that suggest an inner planet of only 17.7+/-5.57 M-circle plus, if coplanarity is assumed for the system.

We present optical and infrared phase-resolved photometry of the magnetic cataclysmic variable EF Eri during a low state. The BVRIJ light curves are very similar in appearance; all exhibit a dip of a few tenths of a magnitude near binary orbital phase 0.5. In contrast, however, the H- and K-band light curves show very large modulations, with maxima at orbital phase 0.5. We show that these modulations are not due to ellipsoidal variations but to the reflection/heating of one face of the very cool secondary star by the white dwarf primary. We find that the dips in the BVRIJ light curves are best modeled by a single hot spot on the white dwarf primary that is self-eclipsed once per orbit. By using an orbital inclination of i = 45°, we find the colatitude of the hot spot is 35° ± 10°, its temperature is 12,000 K, and its radius is 29° ± 15°. To explain the larger minimum seen in the J-band light curve requires that ∼20% of the observed flux be supplied by an additional source of luminosity, which we believe is residual cyclotron emission. To model the observed amplitudes in the H- and K-band light curves requires a very cool irradiated brown dwarf–like secondary star with temperature Teff ≈ 900 K (for i = 45°). The irradiated side of this secondary star, however, has Teff ≲ 1600 K. We present a new K-band spectrum of EF Eri that is consistent with this result. To properly model the light curve of EF Eri will require the incorporation of brown dwarf atmospheres into the Wilson-Divinney program, as well as better estimates for the irradiated limb-darkening coefficients and albedos of such objects. Finally, we present a three-dimensional hydrodynamic model for EF Eri that demonstrates that the accretion stream from the secondary star is almost fully controlled by the magnetic field of the white dwarf primary. This model predicts that the narrow dips observed in the high-state infrared light curves of EF Eri, which nominally should lead the binary in orbital phase, can occur very close to phase 0.0, as required by our light-curve modeling.

Using the HST Fine Guidance Sensor, we have measured a high precision astrometric parallax of the cataclysmic variable EX Hydrae, pi = 15.50 +/- 0.29 mas. From the wavelength-integrated accretion-induced energy flux, we derive a quiescent accretion luminosity for EX Hya of L-acc = (2.6 +/- 0.6) x 10(32) erg s(-1). The quiescent accretion rate then is. (M) over dot(av) = (6.2 +/- 1.5) x 10(-11)(M-1/0.5 M.)(-1.61) M. yr(-1). The time-averaged accretion rate, which includes a small correction for the rare outbursts, is 6% higher. We discuss the system parameters of EX Hya and deduce M-1 = 0.4-0.7 M., M-2 = 0.07-0.10 M., and i = 76.0degrees - 77.6degrees, using recent radial velocity measurements of both components and restrictions imposed by other observational and theoretical constraints. We conclude that the secondary is undermassive, overluminous, and expanded over a ZAMS star of the same mass. Near the upper limit to M-1, the accretion rate of the white dwarf coincides with that due to near-equilibrium angular momentum loss by gravitational radiation and angular momentum transfer from the orbit into the spin-up of the white dwarf. Near the lower mass limit, the correspondingly higher accretion rate requires that either an additional angular momentum loss process is acting besides gravitational radiation or that accretion occurs on a near-adiabatic time scale. The latter possibility would imply that EX Hya is in a transient phase of high mass transfer and the associated spin-up of the white dwarf.