24 research outputs found
A radio-map of the colliding winds in the very massive binary system HD 93129A
Radio observations are an effective tool to discover particle acceleration
regions in colliding-wind binaries, through detection of synchrotron radiation;
these regions are natural laboratories for the study of relativistic particles.
Wind-collision region (WCR) models can reproduce the radio continuum spectra of
massive binaries that contain both thermal and non-thermal radio emission;
however, key constraints for models come from high-resolution imaging. Only
five WCRs have been resolved to date at radio frequencies at milliarcsec (mas)
angular scales. The source HD 93129A, prototype of the very few known O2 I
stars, is a promising target for study: recently, a second massive, early-type
star about 50 mas away was discovered, and a non-thermal radio source detected
in the region. Preliminary long-baseline array data suggest that a significant
fraction of the radio emission from the system comes from a putative WCR. We
sought evidence that HD 93129A is a massive binary system with colliding
stellar winds that produce non-thermal radiation, through spatially resolved
images of the radio emitting regions. We completed observations with the
Australian Long Baseline Array (LBA) to resolve the system at mas angular
resolutions and reduced archival Australia Telescope Compact Array (ATCA) data
to derive the total radio emission. We also compiled optical astrometric data
of the system in a homogeneous way. We reduced historical Hubble Space
Telescope data and obtained absolute and relative astrometry with milliarcsec
accuracy. The astrometric analysis leads us to conclude that the two stars in
HD 93129A form a gravitationally bound system. The LBA data reveal an extended
arc-shaped non-thermal source between the two stars, indicative of a WCR. The
wind momentum-rate ratio of the two stellar winds is estimated. The ATCA data
show a point source with a change in flux level ...Comment: Accepted in Astronomy and Astrophysic
Detecting a small Kuiper Belt object using archival data of HST's Fine Guidance Sensor
The Kuiper Belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper Belt objects. Small, sub-kilometer-sized, Kuiper Belt objects elude direct detection, but the signature of their occultations of background stars should be detectable. Such an occultation event
lasts typically a fraction of a second, thus making it a classical high time-resolution observation. Here we report an analysis of archival data of HST’s Fine Guidance Sensors (FGS), that reveals an occultation by such a small object. The detection introduces the FGS as a valuable HTRA instrument. We discuss the statistical aspects regarding the validation of the detection claim, and its physical implications
Dynamical Masses for Low-Mass Pre-Main Sequence Stars: A Preliminary Physical Orbit for HD 98800 B
We report on Keck Interferometer observations of the double-lined binary (B)
component of the quadruple pre-main sequence (PMS) system HD 98800. With these
interferometric observations combined with astrometric measurements made by the
Hubble Space Telescope Fine Guidance Sensors (FGS), and published radial
velocity observations we have estimated preliminary visual and physical orbits
of the HD 98800 B subsystem. Our orbit model calls for an inclination of 66.8
3.2 deg, and allows us to infer the masses and luminosities of the
individual components. In particular we find component masses of 0.699
0.064 and 0.582 0.051 M_{\sun} for the Ba (primary) and Bb (secondary)
components respectively.
Modeling of the component SEDs finds temperatures and luminosities in
agreement with previous studies, and coupled with the component mass estimates
allows for comparison with PMS models in the low-mass regime with few empirical
constraints. Solar abundance models seem to under-predict the inferred
component temperatures and luminosities, while assuming slightly sub-solar
abundances bring the models and observations into better agreement. The present
preliminary orbit does not yet place significant constraints on existing
pre-main sequence stellar models, but prospects for additional observations
improving the orbit model and component parameters are very good.Comment: 20 pages, 6 figures, ApJ in press; tables 2 and 3 to be included in
ApJ versio
Astrometry with the Wide-Field InfraRed Space Telescope
The Wide-Field InfraRed Space Telescope (WFIRST) will be capable of
delivering precise astrometry for faint sources over the enormous field of view
of its main camera, the Wide-Field Imager (WFI). This unprecedented combination
will be transformative for the many scientific questions that require precise
positions, distances, and velocities of stars. We describe the expectations for
the astrometric precision of the WFIRST WFI in different scenarios, illustrate
how a broad range of science cases will see significant advances with such
data, and identify aspects of WFIRST's design where small adjustments could
greatly improve its power as an astrometric instrument.Comment: version accepted to JATI
Detecting a small Kuiper Belt object using archival data of HST's Fine Guidance Sensor
The Kuiper Belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper Belt objects. Small, sub-kilometer-sized, Kuiper Belt objects elude direct detection, but the signature of their occultations of background stars should be detectable. Such an occultation event
lasts typically a fraction of a second, thus making it a classical high time-resolution observation. Here we report an analysis of archival data of HST’s Fine Guidance Sensors (FGS), that reveals an occultation by such a small object. The detection introduces the FGS as a valuable HTRA instrument. We discuss the statistical aspects regarding the validation of the detection claim, and its physical implications
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The Distance To The Hyades Cluster Based On Hubble Space Telescope Fine Guidance Sensor Parallaxes
Trigonometric parallax observations made with the Hubble Space Telescope (HST) Fine Guidance Sensor (FGS) 3 of seven Hyades members in six fields of view have been analyzed along with their proper motions to determine the distance to the cluster. Knowledge of the convergent point and mean proper motion of the Hyades is critical to the derivation of the distance to the center of the cluster. Depending on the choice of the proper-motion system, the derived cluster center distance varies by 9%. Adopting a reference distance of 46.1 pc or m - M = 3.32, which is derived from the ground-based parallaxes in the General Catalogue of Trigonometric Stellar Parallaxes (1995 edition), the FK5/PPM proper-motion system yields a distance 4% larger, while the Hanson system yields a distance 2% smaller. The HST FGS parallaxes reported here yield either a 14% or 5% larger distance, depending on the choice of the proper-motion system. Orbital parallaxes (Torres et al.) yield an average distance 4% larger than the reference distance. The variation in the distance derived from the HST data illustrates the importance of the proper-motion system and the individual proper motions to the derivation of the distance to the Hyades center; therefore, a full utilization of the HST FGS parallaxes awaits the establishment of an accurate and consistent proper-motion system.NASA HST GTO, HF-1042.01-93A, HF-1046.01-93A, NAS526555Astronom
Astrometry with the WFIRST Wide-Field Imager
The Wide-Field InfraRed Space Telescope (WFIRST) will be capable of delivering precise astrometry for faint sources over the enormous field of view of its main camera, the Wide-Field Imager (WFI). This unprecedented combination will be transformative for the many scientific questions that require precise positions, distances, and velocities of stars. We describe the expectations for the astrometric precision of the WFIRST WFI in different scenarios, illustrate how a broad range of science cases will see significant advances with such data, and identify aspects of WFIRST's design where small adjustments could greatly improve its power as an astrometric instrument
Astrometry with the WFIRST Wide-Field Imager
The Wide-Field InfraRed Space Telescope (WFIRST) will be capable of delivering precise astrometry for faint sources over the enormous field of view of its main camera, the Wide-Field Imager (WFI). This unprecedented combination will be transformative for the many scientific questions that require precise positions, distances, and velocities of stars. We describe the expectations for the astrometric precision of the WFIRST WFI in different scenarios, illustrate how a broad range of science cases will see significant advances with such data, and identify aspects of WFIRST's design where small adjustments could greatly improve its power as an astrometric instrument