159 research outputs found
Periodic radial velocity variations in RU Lupi
Context. RU Lup is a Classical T Tauri star with unusually strong emission
lines, which has been interpreted as manifestations of accretion. Recently,
evidence has accumulated that this star might have a variable radial velocity.
Aims. We intended to investigate in more detail the possible variability in
radial velocity using a set of 68 high-resolution spectra taken at the VLT
(UVES), the AAT (UCLES) and the CTIO (echelle). Methods. Using standard
cross-correlation techniques, we determined the radial velocity of RU Lup. We
analysed these results with Phasedispersion minimization and the Lomb-Scargle
periodogram and searched for possible periodicities in the obtained radial
velocities. We also analysed changes in the absorption line shapes and the
photometric variability of RU Lup. Results. Our analysis indicated that RU Lup
exhibits variations in radial velocity with a periodicity of 3.71 days and an
amplitude of 2.17 km/s. These variations can be explained by the presence of
large spots, or groups of spots, on the surface of RU Lup. We also considered a
low-mass companion and stellar pulsations as alternative sources for these
variations but found these to be unlikely.Comment: 8 pages, 4 figures, Accepted by A&
The Peculiar Periodic YSO WL 4 in ρ Ophiuchus
We present the discovery of 130.87 day periodic near-infrared flux variability for the Class II T Tauri star WL 4 (= 2MASS J16271848-2429059, ISO-Oph 128). Our data are from the 2MASS Calibration Point Source Working Database, and constitute 1580 observations in J, H and K_s of a field in ρ Ophiuchus used to calibrate the 2MASS All-Sky Survey. We identify a light curve for WL 4 with eclipse amplitudes of ~0.4 mag lasting more than one-quarter the period, and color variations in J-H and H-K_s, of ~0.1 mag. The long period cannot be explained by stellar rotation. We propose that WL 4 is a triple YSO system, with an inner binary orbital period of 130.87 days. We posulate that we are observing each component of the inner binary alternately being eclipsed by a circum-binary disk with respect to our line of sight. This system will be useful in investigating terrestrial zone YSO disk properties and dynamics at ~1 Myr
WASP-1: A lithium- and metal-rich star with an oversized planet
In this paper we present our results of a comprehensive spectroscopicanalysis
of WASP-1, the host star to the exoplanet WASP-1b. We derive T_eff = 6110 +/-
45 K, log g = 4.28 +/- 0.15, and [M/H] = 0.23 +/- 0.08, and also a high
abundance of lithium, log n(Li) = 2.91 +/- 0.05. These parameters suggests an
age for the system of 1-3 Gyr and a stellar mass of 1.25-1.35 M_sun. This means
that WASP-1 has properties very similar to those of HD 149026, the host star
for the highest density planet yet detected. Moreover, their planets orbit at
comparable distances and receive comparable irradiating fluxes from their host
stars. However, despite the similarity of WASP-1 with HD 149026, their planets
have strongly different densities. This suggests that gas-giant planet density
is not a simple function of host-star metallicity or of radiation environment
at ages of ~2 Gyr.Comment: Accepted for publication in MNRAS. 6 pages, 4 figure
Unveiling extremely veiled T Tauri stars
Photospheric absorption lines in classical T Tauri stars (CTTS) are weak
compared to normal stars. This so-called veiling is normally identified with an
excess continuous emission formed in shock-heated gas at the stellar surface
below the accretion streams. We have selected four stars (RW Aur A, RU Lup, S
CrA NW and S CrA SE) with unusually strong veiling to make a detailed
investigation of veiling versus stellar brightness and emission line strengths
for comparisons to standard accretion models. We have monitored the stars
photometrically and spectroscopically at several epochs. In standard accretion
models a variable accretion rate will lead to a variable excess emission.
Consequently, the stellar brightness should vary accordingly. We find that the
veiling of absorption lines in these stars is strongly variable and usually so
large that it would require the release of several stellar luminosities of
potential energy. At states of very large line dilution, the correspondingly
large veiling factors derived correlate only weakly with brightness. Moreover,
the emission line strengths violate the expected trend of veiling versus line
strength. The veiling can change dramatically in one night, and is not
correlated with the phase of the rotation periods found for two stars. We show
that in at least three of the stars, when the veiling becomes high, the
photospheric lines become filled-in by line emission, which produces large
veiling factors unrelated to changes in any continuous emission from shocked
regions. We also consider to what extent extinction by dust and electron
scattering in the accretion stream may affect veiling measures in CTTS. We
conclude that the degree of veiling cannot be used as a measure of accretion
rates in CTTS with rich emission line spectra.Comment: Accepted for publication in A&A Letters. New language-edited version.
(4 pages, 3 figures
Welcome back, Polaris the Cepheid
For about 100 years the amplitude of the 4-day pulsation in Polaris has
decreased. We present new results showing a significant increase in the
amplitude based on 4.5 years of continuous monitoring from the ground and with
two satellite missions.Comment: 5 pages; to appear in the proceedings of the "Cool Stars 15" workshop
held at St Andrews, U
Teff and logg dependence of FeH in M-dwarfs
We present synthetic FeH band spectra in the z-filter range for several
M-dwarf models with logg=3.0-5.0 [cgs] and Teff=2800K -3450K. Our aim is to
characterize convective velocities in M-dwarfs and to give a rough estimate of
the range in which 3D-atmosphere treatment is necessary and where 1D-atmosphere
models suffice for the interpretation of molecular spectral features. This is
also important in order to distinguish between the velocity-broadening and the
rotational- or Zeeman-broadening. The synthetic spectra were calculated using
3D CO5BOLD radiative-hydrodynamic (RHD) models and the line synthesis code
LINFOR3D. We used complete 3D-models and high resolution 3D spectral synthesis
for the detailed study of some well isolated FeH lines. The FeH line strength
shows a dependence on surface gravity and effective temperature and could be
employed to measure both quantities in M-type objects. The line width is
related to the velocity-field in the model stars, which depends strongly on
surface gravity. Furthermore, we investigate the velocity-field in the 3D
M-dwarf models together with the related micro- and macro-turbulent velocities
in the 1D case. We also search for effects on the lineshapes.Comment: Cool Stars 15 Conference Proceeding, 4 page
Teff and logg dependence of FeH in M-dwarfs
We present synthetic FeH band spectra in the z-filter range for several
M-dwarf models with logg=3.0-5.0 [cgs] and Teff=2800K -3450K. Our aim is to
characterize convective velocities in M-dwarfs and to give a rough estimate of
the range in which 3D-atmosphere treatment is necessary and where 1D-atmosphere
models suffice for the interpretation of molecular spectral features. This is
also important in order to distinguish between the velocity-broadening and the
rotational- or Zeeman-broadening. The synthetic spectra were calculated using
3D CO5BOLD radiative-hydrodynamic (RHD) models and the line synthesis code
LINFOR3D. We used complete 3D-models and high resolution 3D spectral synthesis
for the detailed study of some well isolated FeH lines. The FeH line strength
shows a dependence on surface gravity and effective temperature and could be
employed to measure both quantities in M-type objects. The line width is
related to the velocity-field in the model stars, which depends strongly on
surface gravity. Furthermore, we investigate the velocity-field in the 3D
M-dwarf models together with the related micro- and macro-turbulent velocities
in the 1D case. We also search for effects on the lineshapes.Comment: Cool Stars 15 Conference Proceeding, 4 page
Modelling Circumbinary Gas Flows in Close T Tauri Binaries
Young close binaries open central gaps in the surrounding circumbinary
accretion disc, but the stellar components may still gain mass from gas
crossing through the gap. It is not well understood how this process operates
and how the stellar components are affected by such inflows. Our main goal is
to investigate how gas accretion takes place and evolves in close T Tauri
binary systems. In particular, we model the accretion flows around two close T
Tauri binaries, V4046 Sgr and DQ Tau, both showing periodic changes in emission
lines, although their orbital characteristics are very different. In order to
derive the density and velocity maps of the circumbinary material, we employ
two-dimensional hydrodynamic simulations with a locally isothermal equation of
state. The flow patterns become quasi-stable after a few orbits in the frame
co-rotating with the system. Gas flows across the circumbinary gap through the
co-rotating Lagrangian points, and local circumstellar discs develop around
both components. Spiral density patterns develop in the circumbinary disc that
transport angular momentum efficiently. Mass is preferentially channelled
towards the primary and its circumstellar disc is more massive than the disc
around the secondary. We also compare the derived density distribution to
observed line profile variability. The line profile variability tracing the gas
flows in the central cavity shows clear similarities with the corresponding
observed line profile variability in V4046 Sgr, but only when the local
circumstellar disc emission was excluded. Closer to the stars normal
magnetospheric accretion may dominate while further out the dynamic accretion
process outlined here dominates. Periodic changes in the accretion rates onto
the stars can explain the outbursts of line emission observed in eccentric
systems such as DQ Tau.Comment: Accepted for publication in MNRA
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