117 research outputs found
Chandra/HETGS Observations of the Capella System: the Primary as a Dominating X-ray Source
Using the Chandra/High Energy Transmission Grating Spectrometer (hereafter
HETGS) we have detected Doppler motion of Capella's X-ray emission lines in the
6 -- 25AA wave-band. The observed motion follows the expected orbital motion of
Capella's primary. This finding implies that the primary G8 III star, not the
secondary G1 III star in the Hertzsprung gap, has been the dominant source of
hot 10^{6.8} -- 10^{7}K plasma at least in the last six years. In addition, the
results demonstrate the long-term stability of the HETGS and demonstrate small
uncertainties of 25 and 33 km/s in the velocity determination with the HEG and
MEG, respectively.Comment: 4 pages, 4 figures, accepted by Astrophysical Journal Letter
Limits on the time variation of the electromagnetic fine-structure constant in the low energy limit from absorption lines in the spectra of distant quasars
Most of the successful physical theories rely on the constancy of few
fundamental quantities (such as the speed of light, , the fine-structure
constant, \alpha, the proton to electron mass ratio, \mu, etc), and
constraining the possible time variations of these fundamental quantities is an
important step toward a complete physical theory. Time variation of \alpha can
be accurately probed using absorption lines seen in the spectra of distant
quasars. Here, we present the results of a detailed many-multiplet analysis
performed on a new sample of Mg II systems observed in high quality quasar
spectra obtained using the Very Large Telescope. The weighted mean value of the
variation in \alpha derived from our analysis over the redshift range 0.4<z<2.3
is \Delta\alpha/\alpha = (-0.06+/-0.06) x 10^{-5}. The median redshift of our
sample (z=1.55) corresponds to a look-back time of 9.7 Gyr in the most favored
cosmological model today. This gives a 3\sigma limit, -2.5 x 10^{-16} yr^-1
<(\Delta\alpha/\alpha\Delta t) <+1.2x10^{-16} yr^-1, for the time variation of
\alpha, that forms the strongest constraint obtained based on high redshift
quasar absorption line systems.Comment: uses revtex, 4 pages 3 figures. Accepted for publication in Physical
Review Letter
Covariant Calculation of General Relativistic Effects in an Orbiting Gyroscope Experiment
We carry out a covariant calculation of the measurable relativistic effects
in an orbiting gyroscope experiment. The experiment, currently known as Gravity
Probe B, compares the spin directions of an array of spinning gyroscopes with
the optical axis of a telescope, all housed in a spacecraft that rolls about
the optical axis. The spacecraft is steered so that the telescope always points
toward a known guide star. We calculate the variation in the spin directions
relative to readout loops rigidly fixed in the spacecraft, and express the
variations in terms of quantities that can be measured, to sufficient accuracy,
using an Earth-centered coordinate system. The measurable effects include the
aberration of starlight, the geodetic precession caused by space curvature, the
frame-dragging effect caused by the rotation of the Earth and the deflection of
light by the Sun.Comment: 7 pages, 1 figure, to be submitted to Phys. Rev.
A Planetary Mass Companion to the K0 Giant HD 17092
We report the discovery of a substellar-mass companion to the K0-giant HD
17092 with the Hobby-Eberly Telescope. In the absence of any correlation of the
observed 360-day periodicity with the standard indicators of stellar activity,
the observed radial velocity variations are most plausibly explained in terms
of a Keplerian motion of a planetary-mass body around the star. With the
estimated stellar mass of 2.3Msun, the minimum mass of the planet is 4.6MJ. The
planet's orbit is characterized by a mild eccentricity of e=0.17 and a
semi-major axis of 1.3 AU. This is the tenth published detection of a planetary
companion around a red giant star. Such discoveries add to our understanding of
planet formation around intermediate-mass stars and they provide dynamical
information on the evolution of planetary systems around post-main sequence
stars.Comment: 13 pages, 3 figures, 2 tables. Submitted to Ap
Probing the cosmological variation of the fine-structure constant: Results based on VLT-UVES sample
Development of fundamental physics relies on the constancy of various
fundamental quantities such as the fine structure constant. Detecting or
constraining the possible time variations of these fundamental physical
quantities is an important step toward a complete understanding of basic
physics. Here we present the results from a detailed many-multiplet analysis
performed using high signal-to-noise ratio, high spectral resolution
observations of 23 Mg II systems detected toward 18 QSOs in the redshift range
0.4<z<2.3 obtained using UVES at the VLT. We validate our procedure and define
the selection criteria that will avoid possible systematics using detail
analysis of simulated data set. We show our Voigt profile fitting code recovers
the variation in \alpha very accurately when we use single component systems
and multiple component systems that are not heavily blended. Spurious
detections are frequently seen when we use heavily blended systems or the
systems with very weak lines. Thus we avoided heavily blended systems and the
systems with Fe II column density < 2x10^12 cm^-2 in the analysis. All steps
involved in the analysis are presented in detail. The weighted mean value of
the variation in \alpha obtained from our analysis over the redshift range
0.4<z<2.3 is {\Delta\alpha/\alpha} = (-0.06+/-0.06)x10^-5. The median redshift
of our sample is 1.55 the 3\sigma upper limit on the time variation of
is -2.5x10^-16 yr^-1< (\Delta\alpha/\alpha\Delta t) <+1.2x10^-16 yr^-1. To our
knowledge this is the strongest constraint from quasar absorption line studies
till date.Comment: 23 pages; A&A style, 15 figures, accepte
A Planet in a 0.6-AU Orbit Around the K0 Giant HD 102272
We report the discovery of one or more planet-mass companions to the K0-giant
HD 102272 with the Hobby-Eberly Telescope. In the absence of any correlation of
the observed periodicities with the standard indicators of stellar activity,
the observed radial velocity variations are most plausibly explained in terms
of a Keplerian motion of at least one planet-mass body around the star. With
the estimated stellar mass of 1.9M, the minimum mass of the confirmed
planet is 5.9M. The planet's orbit is characterized by a small but nonzero
eccentricity of =0.05 and the semi-major axis of 0.61 AU, which makes it the
most compact one discovered so far around GK-giants. This detection adds to the
existing evidence that, as predicted by theory, the minimum size of planetary
orbits around intermediate-mass giants is affected by both planet formation
processes and stellar evolution. The currently available evidence for another
planet around HD 102272 is insufficient to obtain an unambiguous two-orbit
solution.Comment: 10 pages, 5 figure
Revisiting the He II to H I ratio in the Intergalactic Medium
We estimate the He II to H I column density ratio, \eta = N(He II)/N(H I), in
the intergalactic medium towards the high redshift (z_{em} = 2.885) bright
quasar QSO HE 2347-4342 using Voigt-profile fitting of the H I transitions in
the Lyman series and the He II Lyman- transition as observed by the
FUSE satellite. In agreement with previous studies, we find that in
most of the Lyman- forest except in four regions where it is much
smaller () and therefore inconsistent with photo-ionization by
the UV background flux. We detect O VI and C IV absorption lines associated
with two of these regions ( = 2.6346 and 2.6498). We show that if
we constrain the fit of the H I and/or He II absorption profiles with the
presence of metal components, we can accommodate values in the range
15-100 in these systems assuming broadening is intermediate between pure
thermal and pure turbulent. While simple photo-ionization models reproduce the
observed N(O VI)/N(C IV) ratio, they fail to produce low values contrary
to models with high temperature (i.e T K). The Doppler parameters
measured for different species suggest a multiphase nature of the absorbing
regions. Therefore, if low values were to be confirmed, we would favor a
multi-phase model in which most of the gas is at high temperature ( 10
K) but the metals and in particular C IV are due to lower temperature (
few K) photo-ionized gas.Comment: Accepted for publication in the MNRAS (11 pages, 9 figures, 2 tables
Fortnightly Fluctuations in the O-C Diagram of CS 1246
Dominated by a single, large-amplitude pulsation mode, the rapidly-pulsating
hot subdwarf B star CS 1246 is a prime candidate for a long-term O-C diagram
study. We collected nearly 400 hours of photometry with the PROMPT telescopes
over a time span of 14 months to begin looking for secular variations in the
pulse timings. Interestingly, the O-C diagram is dominated by a strong
sinusoidal pattern with a period of 14.1 days and an amplitude of 10.7
light-seconds. Underneath this sine wave is a secular trend implying a decrease
in the 371.7-s pulsational period of Pdot = -1.9 x 10^-11, which we attribute
to the evolution of the star through the H-R diagram. The sinusoidal variation
could be produced by the presence of a low-mass companion, with m sin i ~ 0.12
Msun, orbiting the subdwarf B star at a distance of 20 Rsun. An analysis of the
combined light curve reveals the presence of a low-amplitude first harmonic to
the main pulsation mode.Comment: Accepted for publication in MNRAS. 11 pages, 8 figures, 5 table
The First Extrasolar Planet Discovered with a New Generation High Throughput Doppler Instrument
We report the detection of the first extrasolar planet, ET-1 (HD 102195b),
using the Exoplanet Tracker (ET), a new generation Doppler instrument. The
planet orbits HD 102195, a young star with solar metallicity that may be part
of the local association. The planet imparts radial velocity variability to the
star with a semiamplitude of m s and a period of 4.11 days.
The planetary minimum mass () is .Comment: 42 pages, 11 figures and 5 tables, Accepted for publication in Ap
Design and Construction of Absorption Cells for Precision Radial Velocities in the K Band using Methane Isotopologues
We present a method to optimize absorption cells for precise wavelength
calibration in the near-infrared. We apply it to design and optimize methane
isotopologue cells for precision radial velocity measurements in the K band. We
also describe the construction and installation of two such cells for the
CSHELL spectrograph at NASA's IRTF. We have obtained their high-resolution
laboratory spectra, which we can then use in precision radial velocity
measurements and which can also have other applications. In terms of obtainable
RV precision methane should out-perform other proposed cells, such as the
ammonia cell (NH) recently demonstrated on CRIRES/VLT. The
laboratory spectra of Ammonia and the Methane cells show strong absorption
features in the H band that could also be exploited for precision Doppler
measurements. We present spectra and preliminary radial velocity measurements
obtained during our first-light run. These initial results show that a
precision down to 20-30 m s can be obtained using a wavelength interval
of only 5 nm in the K band and S/N150. This supports the prediction that
a precision down to a few m s can be achieved on late M dwarfs using the
new generation of NIR spectrographs, thus enabling the detection of terrestrial
planets in their habitable zones. Doppler measurements in the NIR can also be
used to mitigate the radial velocity jitter due to stellar activity enabling
more efficient surveys on young active stars.Comment: accepted PASP, Apr 2012 (in press). Preprint version with 36 pages, 9
Figures, 2 Table
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