arXiv subjects

Jerome A. Orosz

Publications and source records attributed to Jerome A. Orosz.

At least 109 records · Page 6Linked to original sources

arXiv2006

2MASS J05162881+2607387: A New Low-Mass Double-Lined Eclipsing Binary

We show that the star known as 2MASS J05162881+2607387 (hereafter J0516) is a double-lined eclipsing binary with nearly identical low-mass components. The spectroscopic elements derived from 18 spectra obtained with the High Resolution Spectrograph on the Hobby-Eberly Telescope during the Fall of 2005 are K_1=88.45 +/- 0.48 km/s and K_2=90.43 +/- 0.60 km/s, resulting in a mass ratio of$q=K_1/K_2 = 0.978 +/- 0.018 and minimum masses of M_1 sin^{3}i=0.775 +/- 0.016 solar masses and M_2 sin^{3}i=0.759 +/- 0.012 solar masses, respectively. We have extensive differential photometry of J0516 obtained over several nights between 2004 January-March (epoch 1) and 2004 October-2005 January plus 2006 January (epoch 2) using the 1m telescope at the Mount Laguna Observatory. The source was roughly 0.1 mag brighter in all three bandpasses during epoch 1 when compared to epoch 2. Also, phased light curves from epoch 1 show considerable out-of-eclipse variability, presumably due to bright spots on one or both stars. In contrast, the phased light curves from epoch 2 show little out-of-eclipse variability. The light curves from epoch 2 and the radial velocity curves were analyzed using our ELC code with updated model atmospheres for low-mass stars. We find the following: M_1=0.787 +/- 0.012 solar masses, R_1=0.788 +/- 0.015 solar radii, M_2=0.770 +/- 0.009 solar masses, and R_2=0.817 +/- 0.010 solar radii. The stars in J0516 have radii that are significantly larger than model predictions for their masses, similar to what is seen in a handful of other well-studied low-mass double-lined eclipsing binaries. We compiled all recent mass and radius determinations from low-mass binaries and determine an empirical mass-radius relation of the form R = 0.0324 + 0.9343M + 0.0374M^2, where the quantities are in solar units.

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arXiv2005

System Parameters of the Transiting Extrasolar Planet HD 209458b

We derive improved system parameters for the HD 209458 system using a model that simultaneously fits both photometric transit and radial velocity observations. The photometry consists of previous Hubble Space Telescope STIS and FGS observations, twelve I-band transits observed between 2001-2003 with the Mt. Laguna Observatory 1m telescope, and six Stromgren b+y transits observed between 2001-2004 with two of the Automatic Photometric Telescopes at Fairborn Observatory. The radial velocities were derived from Keck/HIRES observations. The model properly treats the orbital dynamics of the system, and thus yields robust and physically self-consistent solutions. Our set of system parameters agrees with previously published results though with improved accuracy. For example, applying robust limits on the stellar mass of 0.93-1.20Msun, we find 1.26 < Rplanet < 1.42 Rjup and 0.59 < Mplanet < 0.70 Mjup. We can reduce the uncertainty on these estimates by including a stellar mass-radius relation constraint, yielding Rplanet = 1.35 +/- 0.07 Rjup and Mplanet = 0.66 +/- 0.04 Mjup. Our results verify that the planetary radius is 10-20% larger than predicted by planet evolution models, confirming the need for an additional mechanism to slow the evolutionary contraction of the planet. A revised ephemeris is derived, T0=2452854.82545 + 3.52474554E (HJD), which now contains an uncertainty in the period of 0.016s and should facilitate future searches for planetary satellites and other bodies in the HD 209458 system.

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arXiv2004

Orbital Parameters for the Black Hole Binary XTE J1650-500

(Shortened) We present R-band photometry of the X-ray transient and candidate black hole binary XTE J1650-500 obtained between 2003 May and August with the 6.5m Clay Telescope. A timing analysis of these data reveals a photometric period of 0.3205 +/- 0.0007 days (i.e. 7.63 hr) with a possible alias at 0.3785 days (9.12 hr). Our photometry completely rules out the previously published spectroscopic period of 0.212 days (5.09 hr). Consequently, we reanalyzed the 15 archival ESO/VLT spectra (obtained 2002 June by Sanchez-Fernandez et al.) that were the basis of the previously published spectroscopic period. We used a ``restframe search'' technique that is well suited for cases when the signal-to-noise ratio of individual spectra is low. The results confirmed the photometric period of 0.3205 days, and rule out the alias period near 0.38 days. The best value for the velocity semiamplitude of the companion star is K_2 = 435 +/- 30 km/sec, and the corresponding optical mass function is f(M) = 2.73 +/- 0.56 solar masses. The amplitude of the phased R-band light curve is 0.2 magnitudes, which gives a lower limit to the inclination of 50 +/- 3 degrees in the limiting case of no contribution to the R-band light curve from the accretion disk. If the mass ratio of XTE J1650-500 is similar to the mass ratios of other black hole binaries like A0620-00 or GRS 1124-683 (e.g. Q >~ 10), then our lower limit to the inclination gives an upper limit to the mass of the black hole in XTE J1650-500 of M_1 <~ 7.3 solar masses. However, the mass can be considerably lower if the R-band flux is dominated by the accretion disk. For example, if the accretion disk does contribute 80% of the flux, as our preliminary results suggest, then the black hole mass would be only about 4 solar masses.

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arXiv2004

The X-ray Outburst of H1743-322: High-Frequency QPOs with a 3:2 Frequency Ratio

We observed the 2003 X-ray outburst of H1743-322 in a series of 130 pointed observation with RXTE. We searched individual observations for high-frequency QPOs (HFQPOs) and found only weak or marginal detections near 240 and 160 Hz. We next grouped the observations in several different ways and computed the average power-density spectra (PDS) in a search for further evidence of HFQPOs. This effort yielded two significant results for those observations defined by the presence of low-frequency QPOs (0.1-20 Hz) and an absence of ``band-limited'' power continua: (1) The 9 time intervals with the highest 7-35 keV count rates yielded an average PDS with a QPO at $166 \pm 5$ Hz. ($4.1 σ$; 3--35 keV); and (2) a second group with lower 7-35 keV count rates (26 intervals) produced an average PDS with a QPO at $242 \pm 3$ Hz ($6.0 σ$; 7--35 keV). The ratio of these two frequencies is $1.46 \pm 0.05$. This finding is consistent with results obtained for three other black hole systems that exhibit commensurate HFQPOs in a 3:2 ratio. Furthermore, the occurrence of H1743-322's slower HFQPO at times of higher X-ray luminosity closely resembles the behavior of XTE J1550-564 and GRO J1655-40. We discuss our results in terms of a resonance model that invokes frequencies set by general relativity for orbital motions near a black-hole event horizon.

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arXiv2003

Chandra Detections of Two Quiescent Black Hole X-Ray Transients

Using the Chandra X-ray Observatory, we have detected the black hole transients V4641 Sgr and XTE J1859+226 in their low luminosity, quiescent states. The 0.3-8 keV luminosities are (4.0^(+3.3)_(-2.4))E31 (d/7 kpc)^2 erg/s and (4.2^(+4.8)_(-2.2))E31 (d/11 kpc)^2 erg/s for V4641 Sgr and XTE J1859+226, respectively. With the addition of these 2 systems, 14 out of the 15 transients with confirmed black holes (via compact object mass measurements) now have measured quiescent luminosities or sensitive upper limits. The only exception is GRS 1915+105, which has not been in quiescence since its discovery in 1992. The luminosities for V4641 Sgr and XTE J1859+226 are consistent with the median luminosity of 2E31 erg/s for the systems with previous detections. Our analysis suggests that the quiescent X-ray spectrum of V4641 Sgr is harder than for the other systems in this group, but, due to the low statistical quality of the spectrum, it is not clear if V4641 Sgr is intrinsically hard or if the column density is higher than the interstellar value. Focusing on V4641 Sgr, we compare our results to theoretical models for X-ray emission from black holes in quiescence. Also, we obtain precise X-ray positions for V4641 Sgr and XTE J1859+226 via cross-correlation of the X-ray sources detected near our targets with IR sources in the 2 Micron All-Sky Survey catalog.

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arXiv2003

Ultraviolet Spectra of CV Accretion Disks with Non-Steady T(r) Laws

An extensive grid of synthetic mid- and far-ultraviolet spectra for accretion disks in cataclysmic variables has been presented by Wade and Hubeny (1998). In those models, the disk was assumed to be in steady-state, that is T_eff(r) is specified completely by the mass M_WD and radius R_WD of the accreting white dwarf star and the mass transfer rate M_dot which is constant throughout the disk. In these models, T_eff(r) is proportional to r^{-3/4} except as modified by a cutoff term near the white dwarf. Actual disks may vary from the steady-state prescription for T_eff(r), however, e.g. owing to outburst cycles in dwarf novae M_dot not constant with radius) or irradiation (in which case T_eff in the outer disk is raised above T_steady). To show how the spectra of such disks might differ from the steady case, we present a study of the ultraviolet (UV) spectra of models in which power-law temperature profiles T_eff(r) is proportional to r^{-gamma} with gamma < 3/4 are specified. Otherwise, the construction of the models is the same as in the Wade & Hubeny grid, to allow comparison. We discuss both the UV spectral energy distributions and the appearance of the UV line spectra. We also briefly discuss the eclipse light curves of the non-standard models. Comparison of these models with UV observations of novalike variables suggests that better agreement may be possible with such modified T_eff(r) profiles.

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arXiv2003

Multiwavelength Spectrum of the Black Hole XTE J1118+480 in Quiescence

We present an X-ray/UV/optical spectrum of the black hole primary in the X-ray nova XTE J1118+480 in quiescence at L_x = 4 x 10^{-9} of the Eddington luminosity. The Chandra, HST and MMT spectroscopic observations were performed simultaneously on 2002 January 12 UT. Because this 4.1-hr binary is located at b = 62 deg, the transmission of the ISM is very high (e.g., 70% at 0.3 keV). We present many new results for the quiescent state, such as the first far-UV spectrum and evidence for an 0.35 mag orbital modulation in the near-UV flux. However, the centerpiece of our work is the multiwavelength spectrum of XTE J1118+480, which we argue represents the canonical spectrum of a stellar-mass black hole radiating at L_x = 4 x 10^{-8.5} of the Eddington luminosity. This spectrum is comprised of two apparently disjoint components: a hard X-ray spectrum with a photon index Gamma = 2.02 +/- 0.16, and an optical/UV continuum that resembles a 13,000 K disk blackbody spectrum punctuated by several strong emission lines. We present a model of the source in which the accretion flow has two components: (1) an X-ray-emitting interior region where the flow is advection-dominated, and (2) a thin, exterior accretion disk with a truncated inner edge (R_tr ~ 10^4 Schwarzschild radii) that is responsible for the optical/UV spectrum. For D = 1.8 kpc, the luminosity of the X-ray component is L_x = 3.5 x 10^{30} erg/s (0.3-7 keV); the bolometric luminosity of the optical/UV component is 20 times greater.

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arXiv2002

X-Ray Jet Emission from the Black Hole X-Ray Binary XTE J1550-564 with Chandra in 2000

We have discovered an X-ray jet due to material ejected from the black hole X-ray transient XTE J1550-564. The discovery was first reported by Corbel et al. (Science, 298, 196 and astro-ph/0210224), and here, we present an analysis of the three Chandra observations made between 2000 June and 2000 September. For these observations, a source is present that moves in an eastward direction away from the point source associated with the compact object. The separation between the new source and the compact object changes from 21.3 arcseconds in June to 23.4 arcseconds in September, implying a proper motion of 21.2 +/- 7.2 mas/day, a projected separation of 0.31-0.85 pc and an apparent jet velocity between 0.34 +/- 0.12 and 0.93 +/- 0.32 times the speed of light for a source distance range of d = 2.8-7.6 kpc. These observations represent the first time that an X-ray jet proper motion measurement has been obtained for any accretion powered Galactic or extra-galactic source. While this work deals with the jet to the east of the compact object, the western jet has also been detected in the X-ray and radio bands. The most likely scenario is that the eastern jet is the approaching jet and that the jet material was ejected from the black hole in 1998. Along with a 1998 VLBI proper motion measurement, the Chandra proper motion indicates that the eastern jet decelerated between 1998 and 2000. We present results on the morphology and energy spectrum of the jet. We cannot definitively determine the X-ray emission mechanism, but a synchrotron origin is viable and may provide the simplest explanation for the observations.

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arXiv2002

Inventory of Black Hole Binaries

A small group of X-ray binaries currently provides the best evidence for the existence of stellar-mass black holes. These objects are interacting binary systems where the X-rays arise from accretion of material onto a compact object (i.e. an object with a radius of less than a few hundred km). In some favourable cases, optical studies of the companion star lead to dynamical mass estimates for both components. In 17 cases, the mass of the compact object an X-ray binary has been shown to exceed the maximum mass of a stable neutron star (about 3 solar masses), which leads to the conclusion that these objects are black holes. In this contribution I will review the basic properties of these black hole binaries.

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arXiv2002

X-ray QPOs in Black-Hole Binary Systems

We briefly review the properties and physical consequences of quasiperiodic oscillations (QPOs) seen on many occasions in the X-ray emission from black-hole binary systems. We also report on the discovery of QPOs at 164 and 328 Hz in GRS1915+105. These appear to be analogous to the harmonic systems of high-frequency QPOs seen in XTEJ1550-564 and GROJ1655-40.

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arXiv2002

Evidence for Harmonic Relationships in the High Frequency QPOs of XTE J1550-564 and GRO J1655-40

We continue to investigate the X-ray timing and spectral properties of the black hole binary, XTE J1550-564. For three different groups of observations, we show evidence that two high-frequency QPOs (HFQPOs) occur simultaneously near 184 and 276 Hz. In one group, there is also evidence of a broad feature at 92 Hz. In each case, we can model the QPO profiles while assuming that the central frequencies are related as integral harmonics of a single frequency. We next investigate the X-ray energy spectra, and we find a systematic increase in the strength of the power-law component as the stronger of the two HFQPOs shifts from 276 to 184 Hz. A strikingly similar result is seen for GRO J1655-40 when the stronger HFQPO shifts from 450 to 300 Hz. The fundamental HFQPO frequencies for the two X-ray sources scale inversely with black hole mass, which is consistent with the hypotheses that these HFQPOs represent some oscillation rooted in general relativity (GR) and that the two black holes have similar values of the dimensionless spin parameter. We discuss physical mechanisms that may explain these HFQPOs. In particular, a resonance between the orbital and radial coordinate frequencies in the innner accretion disk, as proposed by Abramowicz & Kluzniak, would imply moderate values for the dimensionless spin parameter (0.1 < a < 0.6) for both black holes.

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arXiv2001

Dynamical Evidence for a Black Hole in the Microquasar XTE J1550-564

Optical spectroscopic observations of the companion star (type G8IV to K4III) in the microquasar system XTE J1550-564 reveal a radial velocity curve with a best fitting spectroscopic period of P_sp = 1.552 +/- 0.010 days and a semiamplitude of K_2 = 349 +/- 12 km/s. The optical mass function is f(M) = 6.86 +/- 0.71 solar masses (1 sigma). We tentatively measure the rotational velocity of the companion star to be V_rot*sin(i) = 90 +/- 10 km/s, which when taken at face value implies a mass ratio of Q = M_1/M_2 = 6.6 (+2.5 / -1.6) (1 sigma), using the above value of K_2. We derive constraints on the binary parameters from simultaneous modelling of the ellipsoidal light and radial velocity curves. We find the most likely value of the mass of the compact object is 9.41 solar masses with a 1 sigma range of 8.36 < M_1 < 10.76 solar masses. If we apply our tentative value of V_rot*sin(i) = 90 +/- 10 km/s as an additional constraint in the ellipsoidal modelling, we find the most likely value of the mass of the compact object is 10.56 solar masses with a 1 sigma range of 9.68 < M_1 < 11.58 solar masses. In either case the mass of the compact object is well above the maximum mass of a stable neutron star, and we therefore conclude XTE J1550-564 contains a black hole.

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arXiv2001

A Multi-Wavelength, Multi-Epoch Study of the Soft X-Ray Transient Prototype, V616 Mon (A0620-00)

We have obtained optical and infrared photometry of the soft x-ray transient prototype V616 Mon (A0620-00). From this photometry, we find a spectral type of K4 for the secondary star in the system, which is consistent with spectroscopic observations. We present J-, H-, and K-band light curves modeled with WD98 and ELC. Combining detailed, independently run models for ellipsoidal variations due to a spotted, non-spherical secondary star, and the observed ultraviolet to infrared spectral energy distribution of the system, we show that the most likely value for the orbital inclination is 40.75 +/- 3 deg. This inclination angle implies a primary black hole mass of 11.0 +/- 1.9 solar masses.

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arXiv2001

The Long-Period Orbit of the Dwarf Nova V630 Cassiopaeia

We present extensive spectroscopy and photometry of the dwarf nova V630 Cassiopeiae. A late-type (K4-5) absorption spectrum is easily detectable, from which we derive the orbital parameters. We find a spectroscopic period of P=2.56387 +/- (4 times 10^{-5}) days and a semiamplitude of K_2=132.9 +/- 4.0 km/s. The resulting mass function, which is a firm lower limit on the mass of the white dwarf, is then f(M)=0.624 +/- 0.056 solar masses. The secondary star is a ``stripped giant'', and using relations between the core mass and the luminosity and the core mass and the radius we derive a lower limit of M_2 > 0.165 solar masses for the secondary star. The rotational velocity of the secondary star is not resolved in our spectra and we place a limit of V_rot*sin(i) < 40 km/s. The long-term light curve shows variations of up to 0.4 mag on short (1-5 days) time scales, and variations of 0.2-0.4 mag on longer (3-9 months) time scales. In spite of these variations, the ellipsoidal light curve of the secondary star is easily seen when the data are folded on the spectroscopic ephemeris. Ellipsoidal models fit to the mean light curve give an inclination in the range 66.96 < i < 78.08 degrees (90 per cent confidence). This inclination range, and the requirement that M_2 > 0.165 solar masses and V_rot*sin(i) < 40 km/s yields a white dwarf mass of M_1=0.977^{+0.168}_{-0.098} solar masses and a secondary star mass of M_2=0.172^{+0.029}_{-0.012} solar masses (90 per cent confidence limits). Our findings confirm the suggestion of Warner (1994), namely that V630 Cas is rare example of a dwarf nova with a long orbital period.

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arXiv2001

A Black Hole in the Superluminal source SAX J1819.3-2525 (V4641 Sgr)

(shortened) Spectroscopic observations of the fast X-ray transient and superluminal jet source SAX J1819.3-2525 (V4641 Sgr) reveal a best fitting period of P_spect=2.81678 +/- 0.00056 days and a semiamplitude of K_2=211.0 +/- 3.1 km/sec. The optical mass function is f(M)=2.74 +/- 0.12 solar masses. We find a photometric period of P_photo=2.81730 +/- 0.00001 days using a light curve measured from photographic plates. The folded light curve resembles an ellipsoidal light curve with two maxima of roughly equal height and two minima of unequal depth per orbital cycle. The secondary star is a late B-type star which has evolved off the main sequence. Using a moderate resolution spectrum (R=7000) we measure T_eff=10500 +/- 200K, log(g)=3.5 +/- 0.1, and V_rot*sin(i)=123 +/- 4 km/sec (1 sigma errors). Assuming synchronous rotation, our measured value of the projected rotational velocity implies a mass ratio of Q=M_1/M_2=1.50 +/- 0.08 (1sigma). The lack of X-ray eclipses implies an upper limit to the inclination of i<70.7 deg. On the other hand, the large amplitude of the folded light curve (about 0.5 mag) implies a large inclination (i>60 deg). Using the above mass function, mass ratio, and inclination range, the mass of the compact object is in the range 8.73 < M_1 < 11.70 solar masses and the mass of the secondary star is in the range 5.49 < M_2 < 8.14 solar masses (90% confidence). The mass of the compact object is well above the maximum mass of a stable neutron star and we conclude that V4641 Sgr contains a black hole.

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arXiv2001

Optical and Infrared Photometry of the Micro-Quasar GRO J1655-40 in Quiescence

We present BVIJK photometry of the black-hole candidate GRO J1655-40 in full quiescence. We report a refined orbital period of 2.62191 +/- 0.00020 days. The light curves are dominated by ellipsoidal variations from the secondary star. We model the light curves with an upgraded code which includes a more accurate treatment of limb darkening. Previous models containing a large cool disk are ruled out, and indeed our data can be fit with a pure ellipsoidal light curve without any disk contribution. In general agreement with previous results, we derive a confidence region of the correlated quantities of inclination and mass ratio, centered on an inclination of 70.2 +/ 1.9 degrees, and mass ratio 2.6 +/- 0.3, resulting in a primary mass M = 6.3 +/- 0.5 Mo (all 95% confidence). The complex limits and errors on these values, and on the possible disk contribution to the light curve, are discussed.

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arXiv2000

The use of the NEXTGEN model atmospheres for cool giants in a light curve synthesis code

We have written a light curve synthesis code that makes direct use of model atmosphere specific intensities, in particular the NEXTGEN model atmosphere grid for cool giants (T_eff <= 6800 K and log(g) <= 3.5, Hauschildt et al. 1999). We point out that these models (computed using spherical geometry) predict a limb darkening behaviour that deviates significantly from a simple linear or two-parameter law (there is less intensity at the limb of the star). The presence of a significantly nonlinear limb darkening law has two main consequences. First, the ellipsoidal light curve computed for a tidally distorted giant using the NEXTGEN intensities is in general different from the light curve computed using the same geometry but with the black body approximation and a one- or two-parameter limb darkening law. In most cases the light curves computed with the NEXTGEN intensities have deeper minima than their black body counterparts. Thus the light curve solutions for binaries with a giant component obtained with models with near linear limb darkening (either black body or plane-parallel model atmosphere intensities) are biased. Observations over a wide wavelength range (i.e. both the optical and infrared) are particularly useful in discriminating between models with nearly linear limb darkening and the NEXTGEN models. Second, we show that rotational broadening kernels for Roche lobe filling (or nearly filling) giants can be significantly different from analytic kernels due to a combination of the nonspherical shape of the star and the radical departure from a simple limb darkening law. As a result, geometrical information inferred from V_rot*sin(i) measurements of cool giants in binary systems are likewise biased.

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arXiv2000

Optical Observations of the Black Hole Candidate XTE J1550-564 During Re-Flare and Quiescence

We report optical monitoring of the soft X-ray transient XTE J1550-564 during the 1999 season (4 January 1999 to 24 August 1999). The first optical observations available in 1999 show that the peak ``re-flare'' brightness had exceeded the peak brightness of the initial optical flare in September 1998 by over half a magnitude. We compare the optical re-flare light curves with the total X-ray flux, the power-law flux and disk flux light curves constructed from the spectral fits to RXTE/PCA data made by Sobczak et al. (1999, 2000). During the first 60 days of the observed optical re-flare, we find no correspondence between the thermal component of the X-rays often associated with a disk and the optical flux -- the former remains essentially flat whereas the latter declines exponentially and exhibits three substantial dips. However, the power law flux is anti-correlated with the optical dips, suggesting that the optical flux may by up-scattered into the X-ray by the hot corona. Periodic modulations were discovered during the final stage of the outburst (May to June), with P=1.546+/-0.038 days, and during quiescence (July and August), with P=1.540+/-0.008 days. The analysis of the combined data set reveals a strong signal for a unique period at P=1.541+/-0.009 days, which we believe to be the orbital period.

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