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NASA NTRS1993

Models of classical and recurrent novae

The behavior of novae may be divided roughly into two separate stages: quiescence and outburst. However, at closer inspection, both stages cannot be separated. It should be attempted to explain features in both stages with a similar model. Various simple models to explain the observed light and spectral observations during post optical maximum activity are conceivable. In instantaneous ejection models, all or nearly all material is ejected in a time that is short compared with the duration of post optical maximum activity. Instantaneous ejection type 1 models are those where the ejected material is in a fairly thin shell, the thickness of which remains small. In the instantaneous ejection type 2 model ('Hubble Flow'), a thick envelope is ejected instantaneously. This envelope remains thick as different parts have different velocities. Continued ejection models emphasize the importance of winds from the nova after optical maximum. Ejection is supposed to occur from one of the components of the central binary, and one can imagine a general swelling of one of the components, so that something resembling a normal, almost stationary, stellar photosphere is observed after optical maximum. The observed characteristics of recurrent novae in general are rather different from those of classical novae, thus, models for these stars need not be the same.

Friedjung, Michael↗

DOE OSTI2014

Discovery of a wide planetary-mass companion to the young M3 star GU PSC

We present the discovery of a comoving planetary-mass companion ∼42'' (∼2000 AU) from a young M3 star, GU Psc, a likely member of the young AB Doradus Moving Group (ABDMG). The companion was first identified via its distinctively red i – z color (>3.5) through a survey made with Gemini-S/GMOS. Follow-up Canada-France-Hawaii Telescope/WIRCam near-infrared (NIR) imaging, Gemini-N/GNIRS NIR spectroscopy and Wide-field Infrared Survey Explorer photometry indicate a spectral type of T3.5 ± 1 and reveal signs of low gravity which we attribute to youth. Keck/Adaptive Optics NIR observations did not resolve the companion as a binary. A comparison with atmosphere models indicates T {sub eff} = 1000-1100 K and log g = 4.5-5.0. Based on evolution models, this temperature corresponds to a mass of 9-13 M {sub Jup} for the age of ABDMG (70-130 Myr). The relatively well-constrained age of this companion and its very large angular separation to its host star will allow its thorough characterization and will make it a valuable comparison for planetary-mass companions that will be uncovered by forthcoming planet-finder instruments such as Gemini Planet Imager and SPHERE 9.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2001

The Discovery of a Second Luminous Low-Mass X-Ray Binary in the Globular Cluster M15

We report an observation by the Chandra X-Ray Observatory of 4U 2127+119, the X-ray source identified with the globular cluster M15. The Chandra observation reveals that 4U 2127+119 is in fact two bright sources, separated by 2.7 arcsec. One source is associated with AC 211, the previously identified optical counterpart to 4U 2127+119, a low-mass X-ray binary (LMXB). The second source, M15 X-2, is coincident with a 19th U magnitude blue star that is 3.3 arcsec from the cluster core. The Chandra count rate of M15 X-2 is 2.5 times higher than that of AC 211. Prior to the 0.5 arcsec imaging capability of Chandra, the presence of two so closely separated bright sources would not have been resolved. The optical counterpart, X-ray luminosity, and spectrum of M15 X-2 are consistent with it also being an LMXB system. This is the first time that two LMXBs have been seen to be simultaneously active in a globular cluster. The discovery of a second active LMXB in M15 solves a long-standing puzzle where the properties of AC 211 appear consistent with it being dominated by an extended accretion disk corona, and yet 4U 2127+119 also shows luminous X-ray bursts requiring that the neutron star be directly visible. The resolution of 4U 2127+119 into two sources suggests that the X-ray bursts did not come from AC 211 but rather from M15 X-2. We discuss the implications of this discovery for understanding the origin and evolution of LMXBs in globular clusters as well as X-ray observations of globular clusters in nearby galaxies.

White, Nicholas E.↗

DOE OSTI2021

Binary Amplitude Reflection Gratings for X-ray Shearing and Hartmann Wavefront Sensors

New, high-coherent-flux X-ray beamlines at synchrotron and free-electron laser light sources rely on wavefront sensors to achieve and maintain optimal alignment under dynamic operating conditions. This includes feedback to adaptive X-ray optics. We describe the design and modeling of a new class of binary-amplitude reflective gratings for shearing interferometry and Hartmann wavefront sensing. Compact arrays of deeply etched gratings illuminated at glancing incidence can withstand higher power densities than transmission membranes and can be designed to operate across a broad range of photon energies with a fixed grating-to-detector distance. Coherent wave-propagation is used to study the energy bandwidth of individual elements in an array and to set the design parameters. We observe that shearing operates well over a ±10% bandwidth, while Hartmann can be extended to ±30% or more, in our configuration. We apply this methodology to the design of a wavefront sensor for a soft X-ray beamline operating from 230 eV to 1400 eV and model shearing and Hartmann tests in the presence of varying wavefront aberration types and magnitudes.

47 OTHER INSTRUMENTATION↗

NASA NTRS1985

On the binary nature of cosmic gamma-ray burst sources

The binary model of gamma ray burst sources wherein the bursts are emitted by a collapsed object in a close-binary stellar system and a small fraction of the gamma radiation is reprocessed into optical radiation in the surface layers of a companion star is considered, and it is concluded that the model is viable. In particular, under the assumption that the optical flashes discovered by Schaefer (1981) and Schaefer et al. (1984) were produced by gamma-ray bursts of about the same intensity as those observed, it is found that nearby binary systems with secondaries whose masses are less than about 0.06 solar mass can fit all the observational constraints for the three optical/gamma-ray pair events.

Rappaport, S. A.↗

DOE OSTI2012

Hadamard multimode optical imaging transceiver

Disclosed is a method and system for simultaneously acquiring and producing results for multiple image modes using a common sensor without optical filtering, scanning, or other moving parts. The system and method utilize the Walsh-Hadamard correlation detection process (e.g., functions/matrix) to provide an all-binary structure that permits seamless bridging between analog and digital domains. An embodiment may capture an incoming optical signal at an optical aperture, convert the optical signal to an electrical signal, pass the electrical signal through a Low-Noise Amplifier (LNA) to create an LNA signal, pass the LNA signal through one or more correlators where each correlator has a corresponding Walsh-Hadamard (WH) binary basis function, calculate a correlation output coefficient for each correlator as a function of the corresponding WH binary basis function in accordance with Walsh-Hadamard mathematical principles, digitize each of the correlation output coefficient by passing each correlation output coefficient through an Analog-to-Digital Converter (ADC), and performing image mode processing on the digitized correlation output coefficients as desired to produce one or more image modes. Some, but not all, potential image modes include: multi-channel access, temporal, range, three-dimensional, and synthetic aperture.

47 OTHER INSTRUMENTATION↗

NASA NTRS2021

RX J0529.8-6556: a BeXRB Pulsar with an Evolving Optical Period and Out of Phase X-ray Outbursts

We report the results of eROSITA and NICER observations of the 2020 June outburst of the Be/X-ray binary pulsar RX J0529.8−6556 in the Large Magellanic Cloud, along with the analysis of archival X-ray and optical data from this source. We find two anomalous features in the system’s behaviour. First, the pulse profile observed by NICER during maximum luminosity is similar to that observed by XMM–Newton in 2000, despite the fact that the X-ray luminosity was different by two orders of magnitude. In contrast, a modest decrease in luminosity in the 2020 observations generated a significant change in pulse profile. Secondly, we find that the historical optical outbursts are not strictly periodic, as would be expected if the outbursts were triggered by periastron passage, as is generally assumed. The optical peaks are also not coincident with the X-ray outbursts. We suggest that this behaviour may result from a misalignment of the Be star disc and the orbital plane, which might cause changes in the timing of the passage of the neutron star through the disc as it processes. We conclude that the orbital period of the source remains unclear.

H Treiber↗

DOE OSTI2010

STUDYING THE PHYSICAL DIVERSITY OF LATE-M DWARFS WITH DYNAMICAL MASSES

We present a systematic study of the physical properties of late-M dwarfs based on high-quality dynamical mass measurements and near-infrared (NIR) spectroscopy. We use astrometry from Keck natural and laser guide star adaptive optics imaging to determine orbits for the late-M binaries LP 349 - 25AB (M7.5+M8), LHS 1901AB (M6.5+M6.5), and Gl 569Bab (M8.5+M9). We find that LP 349 - 25AB (M{sub tot} = 0.120{sup +0.008}{sub -0.007} M{sub sun}) is a pair of young brown dwarfs for which Lyon and Tucson evolutionary models jointly predict an age of 140 {+-} 30 Myr, consistent with the age of the Pleiades. However, at least the primary component seems to defy the empirical Pleiades lithium depletion boundary, implying that the system is in fact older (if the parallax is correct) and that evolutionary models under-predict the component luminosities for this magnetically active binary. We find that LHS 1901AB is a pair of very low-mass stars (M{sub tot} = 0.194{sup +0.025}{sub -0.021} M{sub sun}) with evolutionary model-derived ages consistent with the old age (>6 Gyr) implied by its lack of activity. Our improved orbit for Gl 569Bab results in a higher mass for this binary (M{sub tot} = 0.140{sup +0.009}{sub -0.008} M{sub sun}) compared to previous work (0.125 {+-} 0.007 M{sub sun}). We use these mass measurements along with our published results for 2MASS J2206 - 2047AB (M8+M8) to test four sets of ultracool model atmospheres currently in use. Fitting these models to our NIR integrated-light spectra provides temperature estimates warmer by {approx}250 K than those derived independently from Dusty evolutionary models given the measured masses and luminosities. We propose that model atmospheres are more likely to be the source of this discrepancy, as it would be difficult to explain a uniform temperature offset over such a wide range of masses, ages, and activity levels in the context of evolutionary models. This contrasts with the conclusion of Konopacky et al. that model-predicted masses (given input T{sub eff} and L{sub bol}) are at fault for differences between theory and observations. In addition, we find an opposite (and smaller) mass discrepancy from what they report when we adopt their model-testing approach: masses are too high rather than too low because our T{sub eff} estimates derived from fitting NIR spectra are {approx}650 K higher than their values from fitting broadband photometry alone.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

THE PTF ORION PROJECT: A POSSIBLE PLANET TRANSITING A T-TAURI STAR

We report observations of a possible young transiting planet orbiting a previously known weak-lined T-Tauri star in the 7-10 Myr old Orion-OB1a/25-Ori region. The candidate was found as part of the Palomar Transient Factory (PTF) Orion project. It has a photometric transit period of 0.448413 {+-} 0.000040 days, and appears in both 2009 and 2010 PTF data. Follow-up low-precision radial velocity (RV) observations and adaptive optics imaging suggest that the star is not an eclipsing binary, and that it is unlikely that a background source is blended with the target and mimicking the observed transit. RV observations with the Hobby-Eberly and Keck telescopes yield an RV that has the same period as the photometric event, but is offset in phase from the transit center by Almost-Equal-To - 0.22 periods. The amplitude (half range) of the RV variations is 2.4 km s{sup -1} and is comparable with the expected RV amplitude that stellar spots could induce. The RV curve is likely dominated by stellar spot modulation and provides an upper limit to the projected companion mass of M{sub p}sin i{sub orb} {approx}< 4.8 {+-} 1.2 M{sub Jup}; when combined with the orbital inclination, i{sub orb}, of the candidate planet from modeling of the transit light curve, we find an upper limit on the mass of the planetary candidate of M{sub p} {approx}< 5.5 {+-} 1.4 M{sub Jup}. This limit implies that the planet is orbiting close to, if not inside, its Roche limiting orbital radius, so that it may be undergoing active mass loss and evaporation.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2010

SPITZER OBSERVATIONS OF BLACK HOLE LOW-MASS X-RAY BINARIES: ASSESSING THE NON-STELLAR INFRARED COMPONENT

We have combined ground-based optical and near-infrared data with Spitzer Space Telescope mid-infrared data for five black hole (BH) soft X-ray transients (SXTs) in order to determine the levels of near- and mid-infrared emission from sources other than the secondary star. Mid-infrared emission from an accretion disk, circumbinary dust, and/or a jet could act as sources of near-infrared contamination, thereby diluting ellipsoidal variations of the secondary star and affecting determined BH mass estimates. Based on optical to mid-infrared spectral energy distribution modeling of the five SXTs along with the prototype, V616 Mon, we detected mid-infrared excesses in half of the systems, and suggest that the excesses detected from these systems arise from non-thermal synchrotron jets rather than circumbinary dust disks.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1992

Binaries in globular clusters

Recent observations have shown that globular clusters contain a substantial number of binaries most of which are believed to be primordial. We discuss different successful optical search techniques, based on radial-velocity variables, photometric variables, and the positions of stars in the color-magnitude diagram. In addition, we review searches in other wavelengths, which have turned up low-mass X-ray binaries and more recently a variety of radio pulsars. On the theoretical side, we give an overview of the different physical mechanisms through which individual binaries evolve. We discuss the various simulation techniques which recently have been employed to study the effects of a primordial binary population, and the fascinating interplay between stellar evolution and stellar dynamics which drives globular-cluster evolution.

Hut, Piet↗

DOE OSTI2012

BROADBAND ESO/VISIR-SPITZER INFRARED SPECTROSCOPY OF THE OBSCURED SUPERGIANT X-RAY BINARY IGR J16318-4848

A new class of X-ray binaries has recently been discovered by the high-energy observatory INTEGRAL. It is composed of intrinsically obscured supergiant high-mass X-ray binaries, unveiled by means of multi-wavelength X-ray, optical, near- and mid-infrared observations, in particular, photometric and spectroscopic observations using ESO facilities. However, the fundamental questions about these intriguing sources, namely, their formation, evolution, and the nature of their environment, are still unsolved. Among them, IGR J16318-4848, a compact object orbiting around a supergiant B[e] star, seems to be one of the most extraordinary celestial sources of our Galaxy. We present here new ESO/Very Large Telescope (VLT) VISIR mid-infrared (MIR) spectroscopic observations of this source. First, line diagnostics allow us to confirm the presence of absorbing material (dust and cold gas) enshrouding the whole binary system, and to characterize the nature of this material. Second, by fitting broadband near- to mid-infrared spectral energy distribution, including ESO NTT/SofI, VLT/VISIR, and Spitzer data, with a phenomenological model for sgB[e] stars, we show that the star is surrounded by an irradiated rim heated to a temperature of {approx}3800-5500 K, along with a viscous disk component at an inner temperature of {approx}750 K. VISIR data allow us to exclude the spherical geometry for the dust component. This detailed study will allow us in the future to get better constraints on the formation and evolution of such rare and short-living high-mass X-ray binary systems in our Galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

High-energy Gamma-Ray Activity from V404 Cygni Detected by AGILE during the 2015 June Outburst

The AGILE satellite detected transient high-energy γ -ray emission from the X-ray binary V404 Cygni, during the 2015 June outburst observed in radio, optical, X-ray, and soft γ -ray frequencies. The activity was observed by AGILE in the 50–400 MeV energy band, between 2015 June 24 UT 06:00:00 and 2015 June 26 UT 06:00:00 (MJD 57197.25–57199.25), with a detection significance of ∼4.3 σ . The γ -ray detection, consistent with a contemporaneous observation by Fermi -LAT, is correlated with a bright flare observed at radio and hard X-ray frequencies, and with a strong enhancement of the 511 keV line emission, possibly indicating plasmoid ejections in a lepton-dominated transient jet. The AGILE observations of this binary system are compatible with a microquasar scenario in which transient jets are responsible for the high-energy γ -ray emission.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Radio timing and optical photometry of the black widow system PSR J1953+1846A in the globular cluster M71

We report on the determination of the astrometric, spin, and orbital parameters for PSR J1953+1846 A, a “black widow” binary millisecond pulsar in the globular cluster M71. By using the accurate position and orbital parameters obtained from radio timing, we identified the optical companion in Advanced Camera for Surveys/Hubble Space Telescope images. It turns out to be a faint (m{sub F606W}≳24, m{sub F814W}≳23) and variable star located at only ∼0.″06 from the pulsar timing position. The light curve shows a maximum at the pulsar inferior conjunction and a minimum at the pulsar superior conjunction, thus confirming the association with the system. The shape of the optical modulation suggests that the companion star is heated, likely by the pulsar wind. The comparison with the X-ray light curve possibly suggests the presence of an intra-binary shock due to the interaction between the pulsar wind and the material released by the companion. This is the second identification (after COM-M5C) of an optical companion to a black widow pulsar in a globular cluster. Interestingly, the two companions show a similar light curve and share the same position in the color–magnitude diagram.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

ELECTROMAGNETIC TRANSIENTS POWERED BY NUCLEAR DECAY IN THE TIDAL TAILS OF COALESCING COMPACT BINARIES

We investigate the possibility that long tidal tails formed during compact object mergers may produce optical transients powered by the decay of freshly synthesized r-process material. Precise modeling of the merger dynamics allows for a realistic determination of the thermodynamic conditions in the ejected debris. We combine hydrodynamic and full nuclear network calculations to determine the resultant r-process abundances and the heating of the material by their decays. The subsequent homologous structure is mapped into a radiative transfer code to synthesize emergent model light curves and determine how their properties (variability and color evolution) depend on the mass ratio and orientation of the merging binary. The radiation emanating from the ejected debris, though less spectacular than a typical supernova, should be observable in transient surveys and we estimate the associated detection rates. We find that it is unlikely that photometry alone will be able to distinguish between different binary mass ratios and the nature of the compact objects, emphasizing the need for spectroscopic follow-up of these events. The case for (or against) compact object mergers as the progenitors of short gamma-ray bursts can be tested if such electromagnetic transients are detected (or not) in coincidence with some bursts, although they may be obscured by on-axis afterglows.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Multiwavelength observations of Swift J1753.5–0127

We present contemporaneous X-ray, ultraviolet (UV), optical, and near-infrared observations of the black hole binary system Swift J1753.5–0127 acquired in 2012 October. The UV observations, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope, are the first UV spectra of this system. The dereddened UV spectrum is characterized by a smooth, blue continuum and broad emission lines of C IV and He II. The system was stable in the UV to <10% during our observations. We estimated the interstellar reddening by fitting the 2175 Å absorption feature and fit the interstellar absorption profile of Lyα to directly measure the neutral hydrogen column density along the line of sight. By comparing the UV continuum flux to steady-state thin accretion disk models, we determined upper limits on the distance to the system as a function of black hole mass. The continuum is well fit with disk models dominated by viscous heating rather than irradiation. The broadband spectral energy distribution shows the system has declined at all wavelengths since previous broadband observations in 2005 and 2007. If we assume that the UV emission is dominated by the accretion disk, the inner radius of the disk must be truncated at radii above the innermost stable circular orbit to be consistent with the X-ray flux, requiring significant mass loss from outflows and/or energy loss via advection into the black hole to maintain energy balance.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

High-precision radio and infrared astrometry of LSPM J1314+1320AB. II. Testing pre-main-sequence models at the lithium depletion boundary with dynamical masses

We present novel tests of pre-main-sequence models based on individual dynamical masses for the M7 binary LSPM J1314+1320AB. Joint analysis of Keck adaptive optics astrometric monitoring along with Very Long Baseline Array radio data from a companion paper yield component masses of 92.8 ± 0.6 M {sub Jup} (0.0885 ± 0.0006 M {sub ☉}) and 91.7 ± 1.0 M {sub Jup} (0.0875 ± 0.0010 M {sub ☉}) and a parallactic distance of 17.249 ± 0.013 pc. We find component luminosities consistent with the system being coeval at 80.8 ± 2.5 Myr, according to BHAC15 evolutionary models. The presence of lithium is consistent with model predictions, marking the first test of the theoretical lithium depletion boundary using ultracool dwarfs of known mass. However, we find that the evolutionary model-derived average effective temperature (2950 ± 5 K) is 180 K hotter than that given by a spectral type–T{sub eff} relation based on BT-Settl models (2770 ± 100 K). We suggest that the dominant source of this discrepancy is model radii being too small by ≈13%. In a test mimicking the typical application of models by observers, we derive masses on the H-R diagram using luminosity and BT-Settl temperature. The estimated masses are lower by 46{sub −19}{sup +16}% (2.0σ) than we measure dynamically and would imply that this is a system of ≈50 M {sub Jup} brown dwarfs, highlighting the large systematic errors possible in H-R diagram properties. This is the first time masses have been measured for ultracool (≥M6) dwarfs displaying spectral signatures of low gravity. Based on features in the infrared, LSPM J1314+1320AB appears to have higher gravity than typical Pleiades and AB Dor members, opposite the expectation given its younger age. The components of LSPM J1314+1320AB are now the nearest, lowest mass pre-main-sequence stars with direct mass measurements.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

Resolved Imaging of the AR Puppis Circumbinary Disk

Circumbinary disks are common around post-asymptotic giant branch (post-AGB) stars with a stellar companion on orbital timescales of a few 100 to few 1000 days. The presence of a disk is usually inferred from the system’s spectral energy distribution and confirmed, for a sub-sample, by interferometric observations. We used the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument on the Very Large Telescope to obtain extreme adaptive optics assisted scattered light images of the post-AGB binary system AR Puppis. Data have been obtained in the V, I, and H bands. Our observations have produced the first resolved images of AR Puppis’s circumbinary disk and confirm its edge-on orientation. In our high-angular-resolution and high-dynamic-range images we identify several structural components such as a dark mid-plane, the disk surface, and arc-like features. We discuss the nature of these components and use complementary photometric monitoring to relate them to the orbital phase of the binary system. Because the star is completely obscured by the disk at visible wavelengths, we conclude that the long-term photometric variability of the system must be caused by variable scattering, not extinction, of starlight by the disk over the binary orbit. Finally, we discuss how the short disk lifetimes and fast evolution of the host stars compared to the ages at which protoplanetary disks are typically observed make systems like AR Puppis valuable extreme laboratories to study circumstellar disk evolution and constrain the timescale of dust grain growth during the planet formation process.

79 ASTRONOMY AND ASTROPHYSICS↗