648 research outputs found
Research investigation of electrical discharge fragmentation for protein structure identification Final report
Electrical discharge fragmentation device for determination of bacteria fragmentation pattern
Theoretical Spectra and Light Curves of Close-in Extrasolar Giant Planets and Comparison with Data
We present theoretical atmosphere, spectral, and light-curve models for
extrasolar giant planets (EGPs) undergoing strong irradiation for which {\it
Spitzer} planet/star contrast ratios or light curves have been published (circa
June 2007). These include HD 209458b, HD 189733b, TrES-1, HD 149026b, HD
179949b, and And b. By comparing models with data, we find that a
number of EGP atmospheres experience thermal inversions and have stratospheres.
This is particularly true for HD 209458b, HD 149026b, and And b.
This finding translates into qualitative changes in the planet/star contrast
ratios at secondary eclipse and in close-in EGP orbital light curves. Moreover,
the presence of atmospheric water in abundance is fully consistent with all the
{\it Spitzer} data for the measured planets. For planets with stratospheres,
water absorption features invert into emission features and mid-infrared fluxes
can be enhanced by a factor of two. In addition, the character of near-infrared
planetary spectra can be radically altered. We derive a correlation between the
importance of such stratospheres and the stellar flux on the planet, suggesting
that close-in EGPs bifurcate into two groups: those with and without
stratospheres. From the finding that TrES-1 shows no signs of a stratosphere,
while HD 209458b does, we estimate the magnitude of this stellar flux
breakpoint. We find that the heat redistribution parameter, P, for the
family of close-in EGPs assumes values from 0.1 to 0.4. This paper
provides a broad theoretical context for the future direct characterization of
EGPs in tight orbits around their illuminating stars.Comment: Accepted to Ap. J., provided here in emulateapj format: 28 pages, 8
figures, many with multiple panel
K2 reveals pulsed accretion driven by the 2 Myr old hot Jupiter CI Tau b
CI Tau is a young (~2 Myr) classical T Tauri star located in the Taurus star
forming region. Radial velocity observations indicate it hosts a Jupiter-sized
planet with an orbital period of approximately 9 days. In this work, we analyze
time series of CI Tau's photometric variability as seen by K2. The lightcurve
reveals the stellar rotation period to be ~6.6 d. Although there is no evidence
that CI Tau b transits the host star, a ~9 d signature is also present in the
lightcurve. We believe this is most likely caused by planet-disk interactions
which perturb the accretion flow onto the star, resulting in a periodic
modulation of the brightness with the ~9 d period of the planet's orbit.Comment: Accepted for publication in ApJ Letter
Starspot-induced optical and infrared radial velocity variability in T Tauri star Hubble 4
We report optical (6150 Ang) and K-band (2.3 micron) radial velocities
obtained over two years for the pre-main sequence weak-lined T Tauri star
Hubble I 4. We detect periodic and near-sinusoidal radial velocity variations
at both wavelengths, with a semi-amplitude of 1395\pm94 m/s in the optical and
365\pm80 m/s in the infrared. The lower velocity amplitude at the longer
wavelength, combined with bisector analysis and spot modeling, indicates that
there are large, cool spots on the stellar surface that are causing the radial
velocity modulation. The radial velocities maintain phase coherence over
hundreds of days suggesting that the starspots are long-lived. This is one of
the first active stars where the spot-induced velocity modulation has been
resolved in the infrared.Comment: Accepted for publication in The Astrophysical Journa
Precision radial velocities with CSHELL
Radial velocity identification of extrasolar planets has historically been
dominated by optical surveys. Interest in expanding exoplanet searches to M
dwarfs and young stars, however, has motivated a push to improve the precision
of near infrared radial velocity techniques. We present our methodology for
achieving 58 m/s precision in the K band on the M0 dwarf GJ 281 using the
CSHELL spectrograph at the 3-meter NASA IRTF. We also demonstrate our ability
to recover the known 4 Mjup exoplanet Gl 86 b and discuss the implications for
success in detecting planets around 1-3 Myr old T Tauri stars.Comment: 31 pages, 3 figures, 2 tables, accepted for publication in Ap
Star Spot Induced Radial Velocity Variability in LkCa 19
We describe a new radial velocity survey of T Tauri stars and present the
first results. Our search is motivated by an interest in detecting massive
young planets, as well as investigating the origin of the brown dwarf desert.
As part of this survey, we discovered large-amplitude, periodic, radial
velocity variations in the spectrum of the weak line T Tauri star LkCa 19.
Using line bisector analysis and a new simulation of the effect of star spots
on the photometric and radial velocity variability of T Tauri stars, we show
that our measured radial velocities for LkCa19 are fully consistent with
variations caused by the presence of large star spots on this rapidly rotating
young star. These results illustrate the level of activity-induced radial
velocity noise associated with at least some very young stars. This
activity-induced noise will set lower limits on the mass of a companion
detectable around LkCa 19, and similarly active young stars.Comment: ApJ accepted, 27 pages, 12 figures, aaste
Observations of T Tauri Disks at Sub-AU Radii: Implications for Magnetospheric Accretion and Planet Formation
We determine inner disk sizes and temperatures for four solar-type (1-2
M) classical T Tauri stars (AS 207A, V2508 Oph, AS 205A, and PX Vul)
using 2.2 m observations from the Keck Interferometer. Nearly
contemporaneous near-IR adaptive optics imaging photometry, optical photometry,
and high-dispersion optical spectroscopy are used to distinguish contributions
from the inner disks and central stars in the interferometric observations. In
addition, the spectroscopic and photometric data provide estimates of stellar
properties, mass accretion rates, and disk co-rotation radii. We model our
interferometric and photometric data in the context of geometrically flat
accretion disk models with inner holes, and flared disks with puffed-up inner
walls. Models incorporating puffed-up inner disk walls generally provide better
fits to the data, similar to previous results for higher-mass Herbig Ae stars.
Our measured inner disk sizes are larger than disk truncation radii predicted
by magnetospheric accretion models, with larger discrepancies for sources with
higher mass accretion rates. We suggest that our measured sizes correspond to
dust sublimation radii, and that optically-thin gaseous material may extend
further inward to the magnetospheric truncation radii. Finally, our inner disk
measurements constrain the location of terrestrial planet formation as well as
potential mechanisms for halting giant planet migration.Comment: Accepted for publication in ApJ (May 1, 2005 issue
Amplitude modulation of short-timescale hot spot variability
Funding Information: L.I.B., L.A.P., and J.L. acknowledge support from NASA through an Astrophysics Data Analysis Program grant to Lowell Observatory (grant 80NSSC20K1001). A.C.C. and M.M.J. acknowledge support from the Science and Technology Facilities Council (STFC) consolidated grant No. ST/R00824/1, and the support of the visiting scientist program at Lowell Observatory in 2019 January and 2020 January. Data were obtained using the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.Variability of Classical T Tauri stars (CTTS) occurs over a vast range of timescales. CTTS in particular are subject to variability caused by accretion shocks, which can occur stochastically, periodically, or quasi-periodically on timescales over a few days. The detectability of young planets within these systems is likely hampered by activity; therefore, it is essential that we understand the origin of young star variability over a range of timescales to help disentangle stellar activity from signatures of planetary origin. We present an analysis of the stochastic small-amplitude photometric variability in the K2 lightcurve of CI Tau occurring on timescales of ≲1 day. We find the amplitude of this variability exhibits the same periodic signatures as detected in the large-amplitude variability, indicating that the physical mechanism modulating these brightness features is the same. The periods detected are also in agreement with the rotation period of the star (∼6.6 days) and the orbital period of the planet (∼9.0 days) known to drive pulsed accretion onto the star.PostprintPeer reviewe
On detectability of Zeeman broadening in optical spectra of F- and G-dwarfs
We investigate the detectability of Zeeman broadening in optical Stokes I
spectra of slowly rotating sun-like stars. To this end, we apply the LTE
spectral line inversion package SPINOR to very-high quality CES data and
explore how fit quality depends on the average magnetic field, Bf .
One-component (OC) and two-component (TC) models are adopted. In OC models, the
entire surface is assumed to be magnetic. Under this assumption, we determine
formal 3{\sigma} upper limits on the average magnetic field of 200 G for the
Sun, and 150 G for 61 Vir (G6V). Evidence for an average magnetic field of ~
500 G is found for 59 Vir (G0V), and of ~ 1000 G for HD 68456 (F6V). A
distinction between magnetic and non-magnetic regions is made in TC models,
while assuming a homogeneous distribution of both components. In our TC
inversions of 59 Vir, we investigate three cases: both components have equal
temperatures; warm magnetic regions; cool magnetic regions. Our TC model with
equal temperatures does not yield significant improvement over OC inversions
for 59 Vir. The resulting Bf values are consistent for both. Fit quality is
significantly improved, however, by using two components of different
temperatures. The inversions for 59 Vir that assume different temperatures for
the two components yield results consistent with 0 - 450 G at the formal
3{\sigma} confidence level. We thus find a model dependence of our analysis and
demonstrate that the influence of an additional temperature component can
dominate over the Zeeman broadening signature, at least in optical data.
Previous comparable analyses that neglected effects due to multiple temperature
components may be prone to the same ambiguities.Comment: 18 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
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