147 research outputs found
Candidate selection for the FLAMINGOS-2 galactic center survey
We present a JHK_s catalog of a 20'×20' region around the Galactic Center observed with the ISPI camera on the 4 m CTIO telescope. The data is being used to select targets for the FLAMINGOS-2 Galactic Center Survey, which will take near-infrared spectra of thousands of GC sources in an effort to identify and characterize the unique X-ray binary source population in this region
A Rapidly Varying Red Supergiant X-Ray Binary in the Galactic Center
We analyzed multiwavelength observations of the previously identified Galactic center X-ray binary CXO 174528.79–290942.8 (XID 6592) and determine that the near-infrared counterpart is a red supergiant based on its spectrum and luminosity. Scutum X-1 is the only previously known X-ray binary with a red supergiant donor star and closely resembles XID 6592 in terms of X-ray luminosity (L X), absolute magnitude, and IR variability (L IR,var), supporting the conclusion that XID 6592 contains a red supergiant donor star. The XID 6592 infrared counterpart shows variability of ~0.5 mag in the Wide-field Infrared Survey Explorer-1 band (3.4 μm) on timescales of a few hours. Other infrared data sets also show large-amplitude variability from this source at earlier epochs but do not show significant variability in recent data. We do not expect red supergiants to vary by ~50% in luminosity over these short timescales, indicating that the variability should be powered by the compact object. However, the X-ray luminosity of this system is typically ~1000× less than the variable luminosity in the infrared and falls below the Chandra detection limit. While X-ray reprocessing can produce large-amplitude fast infrared variability, it typically requires LX >> LIR,var to do so, indicating that another process must be at work. We suggest that this system may be a supergiant fast X-ray transient (SFXT), and that a large (~1038 ergs s−1), fast (102-4 s) X-ray flare could explain the rapid IR variability and lack of a long-lasting X-ray outburst detection. SFXTs are normally associated with blue supergiant companions, so if confirmed, XID 6592 would be the first red supergiant SFXT, as well as the second X-ray red supergiant binary.A.M. acknowledges support from the Generalitat Valenciana through the grant BEST/2015/242 and from the Ministerio de Educación, Cultura y Deporte through the grant PRX15/00030
The Path to Buried Treasure: Paving the Way to the FLAMINGOS-2 Galactic Center Survey with IR and X-ray Observations
I describe the IR and X-ray campaign we have undertaken to determine the
nature of the faint discrete X-ray source population discovered by Chandra in
the Galactic Center. These results will provide the input to the FLAMINGOS-2
Galactic Center Survey (F2GCS). With FLAMINGOS-2's multi-object IR spectrograph
we will obtain 1000s of IR spectra of candidate X-ray source counterparts,
allowing us to efficiently identify the nature of these sources, and thus
dramatically increase the number of known X-ray binaries and CVs in the Milky
Way.Comment: To be published in Proceedings of 'A Population Explosion: The Nature
and Evolution of X-ray Binaries in Diverse Environments', 28 Oct - 2 Nov, St.
Pete Beach, FL; eds. R.M. Bandyopadhyay, S. Wachter, D. Gelino, C.R. Gelino;
AIP Conference Proceedings Serie
Exploring a New Population of Compact Objects: X-ray and IR Observations of the Galactic Centre
I describe the IR and X-ray observational campaign we have undertaken for the
purpose of determining the nature of the faint discrete X-ray source population
discovered by Chandra in the Galactic Center (GC). Data obtained for this
project includes a deep Chandra survey of the Galactic Bulge; deep, high
resolution IR imaging from VLT/ISAAC, CTIO/ISPI, and the UKIDSS Galactic Plane
Survey (GPS); and IR spectroscopy from VLT/ISAAC and IRTF/SpeX. By
cross-correlating the GC X-ray imaging from Chandra with our IR surveys, we
identify candidate counterparts to the X-ray sources via astrometry. Using a
detailed IR extinction map, we are deriving magnitudes and colors for all the
candidates. Having thus established a target list, we will use the multi-object
IR spectrograph FLAMINGOS-2 on Gemini-South to carry out a spectroscopic survey
of the candidate counterparts, to search for emission line signatures which are
a hallmark of accreting binaries. By determining the nature of these X-ray
sources, this FLAMINGOS-2 Galactic Center Survey will have a dramatic impact on
our knowledge of the Galactic accreting binary population.Comment: 4 pages, 2 figures, to appear in the Proceedings of The Second
Kolkata Conference on Observational Evidence for Black Holes in the
Universe'', ed. S. Charkrabarti, Kolkata, India; AIP Conf. Serie
Measuring Stellar Radial Velocities with a Dispersed Fixed-Delay Interferometer
We demonstrate the ability to measure precise stellar barycentric radial
velocities with the dispersed fixed-delay interferometer technique using the
Exoplanet Tracker (ET), an instrument primarily designed for precision
differential Doppler velocity measurements using this technique. Our
barycentric radial velocities, derived from observations taken at the KPNO 2.1
meter telescope, differ from those of Nidever et al. by 0.047 km/s (rms) when
simultaneous iodine calibration is used, and by 0.120 km/s (rms) without
simultaneous iodine calibration. Our results effectively show that a Michelson
interferometer coupled to a spectrograph allows precise measurements of
barycentric radial velocities even at a modest spectral resolution of R ~ 5100.
A multi-object version of the ET instrument capable of observing ~500 stars per
night is being used at the Sloan 2.5 m telescope at Apache Point Observatory
for the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS),
a wide-field radial velocity survey for extrasolar planets around TYCHO-2 stars
in the magnitude range 7.6<V<12. In addition to precise differential
velocities, this survey will also yield precise barycentric radial velocities
for many thousands of stars using the data analysis techniques reported here.
Such a large kinematic survey at high velocity precision will be useful in
identifying the signature of accretion events in the Milky Way and
understanding local stellar kinematics in addition to discovering exoplanets,
brown dwarfs and spectroscopic binaries.Comment: 9 pages, 4 figures. Accepted for publication in Ap
Measuring Stellar Radial Velocities with a Dispersed Fixed-Delay Interferometer
We demonstrate the ability to measure precise stellar barycentric radial
velocities with the dispersed fixed-delay interferometer technique using the
Exoplanet Tracker (ET), an instrument primarily designed for precision
differential Doppler velocity measurements using this technique. Our
barycentric radial velocities, derived from observations taken at the KPNO 2.1
meter telescope, differ from those of Nidever et al. by 0.047 km/s (rms) when
simultaneous iodine calibration is used, and by 0.120 km/s (rms) without
simultaneous iodine calibration. Our results effectively show that a Michelson
interferometer coupled to a spectrograph allows precise measurements of
barycentric radial velocities even at a modest spectral resolution of R ~ 5100.
A multi-object version of the ET instrument capable of observing ~500 stars per
night is being used at the Sloan 2.5 m telescope at Apache Point Observatory
for the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS),
a wide-field radial velocity survey for extrasolar planets around TYCHO-2 stars
in the magnitude range 7.6<V<12. In addition to precise differential
velocities, this survey will also yield precise barycentric radial velocities
for many thousands of stars using the data analysis techniques reported here.
Such a large kinematic survey at high velocity precision will be useful in
identifying the signature of accretion events in the Milky Way and
understanding local stellar kinematics in addition to discovering exoplanets,
brown dwarfs and spectroscopic binaries.Comment: 9 pages, 4 figures. Accepted for publication in Ap
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