91 research outputs found
Contemporaneous broad-band photometry and H observations of T Tauri stars
The study of contemporaneous variations of the continuum flux and emission
lines is of great importance to understand the different astrophysical
processes at work in T Tauri stars. In this paper we present the results of a
simultaneous and H photometric monitoring, contemporaneous to
medium-resolution spectroscopy of six T Tauri stars in the Taurus-Auriga star
forming region. We have characterized the H photometric system using
synthetic templates and the contemporaneous spectra of the targets. We show
that we can achieve a precision corresponding to 23 \AA\ in the H
equivalent width, in typical observing conditions. The spectral analysis has
allowed us to determine the basic stellar parameters and the values of
quantities related to the accretion. In particular, we have measured a
significant veiling only for the three targets with the strongest H
emission (T Tau, FM Tau, and DG Tau). The broad-band photometric variations are
found to be in the range 0.050.70 mag and are often paired to variations in
the H intensity, which becomes stronger when the stellar continuum is
weaker. In addition, we have mostly observed a redder and a bluer
color as the stars become fainter. For most of the targets, the timescales of
these variations seem to be longer than the rotation period. One exception is T
Tau, for which the broad-band photometry varies with the rotation period. The
most plausible interpretation of these photometric and H variations is
that they are due to non-stationary mass accretion onto the stars, but
rotational modulation can play a major role in some cases.Comment: 21 pages, 11 figures, accepted for publication in Acta Astronomic
A spectroscopic survey of the youngest field stars in the solar neighborhood: II. the optically faint sample
Star formation in the solar neighborhood is mainly traced by young stars in
open clusters, associations and in the field, which can be identified by their
X-ray emission. The determination of stellar parameters for the counterparts of
X-ray sources is crucial for their study. This work extends the spectroscopic
study of the RasTyc sample, based on TYCHO and RASS catalogs, to stars fainter
than V=9.5 mag. We acquired 625 high-resolution spectra for 443 targets with
four different instruments in the Northern hemisphere. The radial and
rotational velocity (vsini) of our targets are measured by means of the
cross-correlation technique, which is also helpful to discover binaries and
multiple systems. We use the code ROTFIT for determining the atmospheric
parameters and vsini of the single stars and SB1 systems. For these objects, we
also measured the equivalent widths of the H and LiI-6708\AA\ lines,
which enables us to derive their chromospheric activity level and lithium
abundance. We make use of Gaia DR1 parallaxes and proper motions for locating
the targets in the HR diagram and for computing the space velocity components
of the youngest objects. We find a remarkable fraction (>35%) of binaries and
multiple systems. Our sample is mostly (60%) composed of stars younger than the
members of the UMa cluster. We identify 42 very young stars, which lie above or
very close to the Pleiades upper envelope of the lithium abundance. A
significant fraction (12%) of giants/subgiants stars is also present in our
sample. Some of them are also lithium rich (A(Li)>1.4).Comment: 47 pages, 10 figures, accepted by A&
CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOS
Context. CARMENES is a stabilised, high-resolution, double-channel
spectrograph at the 3.5 m Calar Alto telescope. It is optimally designed for
radial-velocity surveys of M dwarfs with potentially habitable Earth-mass
planets. Aims. We prepare a list of the brightest, single M dwarfs in each
spectral subtype observable from the northern hemisphere, from which we will
select the best planet-hunting targets for CARMENES. Methods. In this first
paper on the preparation of our input catalogue, we compiled a large amount of
public data and collected low-resolution optical spectroscopy with CAFOS at the
2.2 m Calar Alto telescope for 753 stars. We derived accurate spectral types
using a dense grid of standard stars, a double least-squares minimisation
technique, and 31 spectral indices previously defined by other authors.
Additionally, we quantified surface gravity, metallicity, and chromospheric
activity for all the stars in our sample. Results. We calculated spectral types
for all 753 stars, of which 305 are new and 448 are revised. We measured
pseudo-equivalent widths of Halpha for all the stars in our sample, concluded
that chromospheric activity does not affect spectral typing from our indices,
and tabulated 49 stars that had been reported to be young stars in open
clusters, moving groups, and stellar associations. Of the 753 stars, two are
new subdwarf candidates, three are T Tauri stars, 25 are giants, 44 are K
dwarfs, and 679 are M dwarfs. Many of the 261 investigated dwarfs in the range
M4.0-8.0 V are among the brightest stars known in their spectral subtype.
Conclusions. This collection of low-resolution spectroscopic data serves as a
candidate target list for the CARMENES survey and can be highly valuable for
other radial-velocity surveys of M dwarfs and for studies of cool dwarfs in the
solar neighbourhood.Comment: A&A, in pres
Discovery of "isolated" comoving T Tauri stars in Cepheus
During the course of a large spectroscopic survey of X-ray active late-type
stars in the solar neighbourhood, we discovered four lithium-rich stars packed
within just a few degrees on the sky. These very young stars are projected
several degrees away from the Cepheus-Cassiopea clouds, in front of an area
void of interstellar matter. As such, they are very good "isolated" T Tauri
star candidates. We acquired high-resolution optical spectra as well as
photometric data allowing us to investigate in detail their nature and physical
parameters with the aim of testing the "runaway" and "in-situ" formation
scenarios. We derive accurate radial and rotational velocities and perform an
automatic spectral classification. The spectral subtraction technique is used
to infer chromospheric activity level in the H-alpha line core and clean the
spectra of photospheric lines before measuring the equivalent width of the
lithium absorption line. Both physical (lithium content, magnetic activity) and
kinematical indicators show that all stars are very young (ages in the range
10-30 Myr). In particular, the spectral energy distribution of TYC4496-780-1
displays a strong near- and far-infrared excess, typical of T Tauri stars still
surrounded by an accretion disc. They also share the same Galactic motion,
proving that they form a homogeneous moving group of stars with the same
origin. The most plausible explanation of how these "isolated" T Tauri stars
formed is the "in-situ" model, although accurate distances are needed to
clarify their connection with the Cepheus-Cassiopeia complex
The Gaia-ESO Survey: membership and Initial Mass Function of the Gamma Velorum cluster
Understanding the properties of young open clusters, such as the Initial Mass
Function (IMF), star formation history and dynamic evolution, is crucial to
obtain reliable theoretical predictions of the mechanisms involved in the star
formation process. We want to obtain a list, as complete as possible, of
confirmed members of the young open cluster Gamma Velorum, with the aim of
deriving general cluster properties such as the IMF. We used all available
spectroscopic membership indicators within the Gaia-ESO public archive together
with literature photometry and X-ray data and, for each method, we derived the
most complete list of candidate cluster members. Then, we considered
photometry, gravity and radial velocities as necessary conditions to select a
subsample of candidates whose membership was confirmed by using the lithium and
H lines and X-rays as youth indicators. We found 242 confirmed and 4
possible cluster members for which we derived masses using very recent stellar
evolutionary models. The cluster IMF in the mass range investigated in this
study shows a slope of for and
for and is consistent with a standard
IMF. The similarity of the IMF of the young population around Vel to
that in other star forming regions and the field suggests it may have formed
through very similar processes.Comment: Accepted for publication in A&A; 18 pages, 11 figures, 5 table
The Gaia-ESO Survey: Chromospheric Emission, Accretion Properties, and Rotation in Velorum and Chamaeleon I
We use the fundamental parameters delivered by the GES consortium in the
first internal data release to select the members of Vel and Cha I
among the UVES and GIRAFFE spectroscopic observations. A total of 140
Vel members and 74 Cha I members were studied. We calculated stellar
luminosities through spectral energy distributions, while stellar masses were
derived by comparison with evolutionary tracks. The spectral subtraction of
low-activity and slowly rotating templates, which are rotationally broadened to
match the of the targets, enabled us to measure the equivalent widths
(EWs) and the fluxes in the H and H lines. The H line
was also used for identifying accreting objects and for evaluating the mass
accretion rate (). The distribution of for the
members of Vel displays a peak at about 10 km s with a tail
toward faster rotators. There is also some indication of a different
distribution for the members of its two kinematical populations. Only a handful
of stars in Vel display signatures of accretion, while many more
accretors were detected in the younger Cha~I. Accreting and active stars occupy
two different regions in a -flux diagram and we propose a
criterion for distinguishing them. We derive in the ranges
-yr and -yr
for Vel and Cha I accretors, respectively. We find less scatter in the
relation derived through the H EWs, when
compared to the H diagnostics, in agreement with other authors
The magnetically-active, low-mass, triple system WDS 19312+3607
Aims: We investigated in detail the system WDS 19312+3607, whose primary is
an active M4.5Ve star previously thought to be young (tau ~ 300-500 Ma) based
on high X-ray luminosity. Methods: We collected intermediate- and
low-resolution optical spectra taken with 2 m-class telescopes, photometric
data from the to 8 mum bands, and eleven astrometric epochs with a time
baseline of over 56 years for the two components in the system, G 125-15 and G
125-14. Results: We derived M4.5V spectral types for both stars, confirmed
their common proper motion, estimated the heliocentric distance and projected
physical separation, determined the galactocentric space velocities, and
deduced a most-probable age older than 600 Ma. We discovered that the primary,
G 125-15, is in turn an inflated, double-lined, spectroscopic binary with a
short period of photometric variability of P ~ 1.6 d, which we associated to
orbital synchronisation. The observed X-ray and Halpha emissions, photometric
variability, and abnormal radius and effective temperature of G 125-15 AB
indicate strong magnetic activity, possibly due to fast rotation. Besides, the
estimated projected physical separation between G 125-15 AB and G 125-14 of
about 1200 AU makes WDS 19312+3607 to be one of the widest systems with
intermediate M-type primaries. Conclusions: G 125-15 AB is a nearby (d ~ 26
pc), bright (J ~ 9.6 mag), active spectroscopic binary with a single
proper-motion companion of the same spectral type at a wide separation. They
are thus ideal targets for specific follow-ups to investigate wide and close
multiplicity or stellar expansion and surface cooling due to reduced convective
efficiency.Comment: A&A, in pres
Integrating genomic information and productivity and climate-adaptability traits into a regional white spruce breeding program
Tree improvement programs often focus on improving productivity-related traits; however, under present climate change scenarios, climate change-related (adaptive) traits should also be incorporated into such programs. Therefore, quantifying the genetic variation and correlations among productivity and adaptability traits, and the importance of genotype by environment interactions, including defense compounds involved in biotic and abiotic resistance, is essential for selecting parents for the production of resilient and sustainable forests. Here, we estimated quantitative genetic parameters for 15 growth, wood quality, drought resilience, and monoterpene traits for Picea glauca (Moench) Voss (white spruce). We sampled 1,540 trees from three open-pollinated progeny trials, genotyped with 467,224 SNP markers using genotyping-by-sequencing (GBS). We used the pedigree and SNP information to calculate, respectively, the average numerator and genomic relationship matrices, and univariate and multivariate individual-tree models to obtain estimates of (co)variance components. With few site-specific exceptions, all traits examined were under genetic control. Overall, higher heritability estimates were derived from the genomic- than their counterpart pedigree-based relationship matrix. Selection for height, generally, improved diameter and water use efficiency, but decreased wood density, microfibril angle, and drought resistance. Genome-based correlations between traits reaffirmed the pedigree-based correlations for most trait pairs. High and positive genetic correlations between sites were observed (average 0.68), except for those pairs involving the highest elevation, warmer, and moister site, specifically for growth and microfibril angle. These results illustrate the advantage of using genomic information jointly with productivity and adaptability traits, and defense compounds to enhance tree breeding selection for changing climate.Instituto de Recursos BiológicosFil: Cappa, Eduardo Pablo. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Recursos Biológicos; ArgentinaFil: Cappa, Eduardo Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Klutsch, Jenifer G. University of Alberta; Department of Renewable Resources; CanadaFil: Sebastian-Azcona, Jaime. University of Alberta; Department of Renewable Resources; CanadaFil: Ratchiffe, Blaise. University of British Columbia. Faculty of Forestry. Department of Forest and Conservation Sciences; CanadáFil: Xiaojing, Wei. University of Alberta; Department of Renewable Resources; CanadaFil: Da Ros, Letitia. University of British Columbia. Faculty of Forestry. Department of Wood Science; CanadáFil: Yang, Liu. University of British Columbia. Faculty of Forestry. Department of Forest and Conservation Sciences; CanadáFil: Chen, Charles. Oklahoma State University. Department of Biochemistry and Molecular Biology; Estados UnidosFil: Benowicz, Andy. Alberta Agriculture and Forestry. Forest Stewardship and Trade Branch; CanadáFil: Sadoway, Shane. Blue Ridge Lumber Inc.; CanadáFil: Mansfield, Shawn D. University of British Columbia. Faculty of Forestry. Department of Wood Science; CanadáFil: Erbilgin, Nadir. University of Alberta; Department of Renewable Resources; CanadaFil: Thomas, Barb R. University of Alberta; Department of Renewable Resources; CanadaFil: El-Kassaby, Yousry A. University of British Columbia. Faculty of Forestry. Department of Forest and Conservation Sciences; Canad
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