29 research outputs found
Spectral energy distribution for GJ406
Original article can be found at: http://www.aanda.org/----Copyright The European Southern ObservatoryPeer reviewe
Masses, Oxygen and Carbon abundances in CHEPS dwarf stars
Reproduced with permission from Astronomy & Astrophysics. © 2019 ESOContext. We report the results from the determination of stellar masses, carbon, and oxygen abundances in the atmospheres of 107 stars from the Calan-Hertfordshire Extrasolar Planet Search (CHEPS) programme. Our stars are drawn from a population with a significantly super-solar metallicity. At least 10 of these stars are known to host orbiting planets. Aims. In this work, we set out to understand the behaviour of carbon and oxygen abundance in stars with different spectral classes, metallicities, and V sin i within the metal-rich stellar population. Methods. Masses of these stars were determined using data from Gaia DR2. Oxygen and carbon abundances were determined by fitting the absorption lines. We determined oxygen abundances with fits to the 6300.304 Å O I line, and we used 3 lines of the C I atom and 12 lines of the C 2 molecule for the determination of carbon abundances. Results. We determine masses and abundances of 107 CHEPS stars. There is no evidence that the [C/O] ratio depends on V sin i or the mass of the star within our constrained range of masses, i.e. 0.82 5 km s -1) are massive stars.Peer reviewedFinal Published versio
Metallicity, temperature, and gravity scales of M subdwarfs
The aim of the project is to define a metallicity/gravity/temperature scale
vs spectral types for metal-poor M dwarfs.
We obtained intermediate-resolution ultraviolet (R~3300), optical (R~5400),
and near-infrared (R~3900) spectra of 43 M subdwarfs (sdM), extreme subdwarfs
(esdM), and ultra-subdwarfs (usdM) with the X-shooter spectrograph on the
European Southern Observatory Very Large Telescope. We compared our atlas of
spectra to the latest BT-Settl synthetic spectral energy distribution over a
wide range of metallicities, gravities, and effective temperatures to infer the
physical properties for the whole M dwarf sequence (M0--M9.5) at sub-solar
metallicities and constrain the latest state-of-the-art atmospheric models.
The BT-Settl models reproduce well the observed spectra across the 450-2500
nm wavelength range except for a few regions. We find that the best fits are
obtained for gravities of log(g) = 5.0-5.5 dex for the three metal classes. We
infer metallicities of [Fe/H] = -0.5, -1.5, and -2.0+/-0.5 dex and effective
temperatures of 3700-2600 K, 3800-2900 K, and 3700-2900 K for subdwarfs,
extreme subdwarfs, and ultra-subdwarfs, respectively. Metal-poor M dwarfs tend
to be warmer by about 200+/-100 K and exhibit higher gravity than their
solar-metallicity counterparts. We derive abundances of several elements (Fe,
Na, K, Ca, Ti) for our sample but cannot describe their atmospheres with a
single metallicity parameter. Our metallicity scale expands the current scales
available for midly metal-poor planet-host low-mass stars. Our compendium of
moderate-resolution spectra covering the 0.45--2.5 micron range represents an
important legacy value for large-scale surveys and space missions to come.Comment: 31 pages, 4 pages, 4 tables + 1 appendix with 12 figures and 5
tables. Accepted for publication in A&A. Version prior to language editio
A hot Jupiter transiting a mid-K dwarf found in the pre-OmegaCam Transit Survey
We describe the pre-OmegaTranS project, a deep survey for transiting
extra-solar planets in the Carina region of the Galactic Disk. In 2006-2008 we
observed a single dense stellar field with a very high cadence of ~2min using
the ESO Wide Field Imager at the La Silla Observatory. Using the Astronomical
Wide-field System for Europe and the Munich Difference Imaging Analysis
pipeline, a module that has been developed for this project, we created the
light curves of 16000 stars with more than 4000 data points which we searched
for periodic transit signals using a box-fitting least-squares detection
algorithm. All light curves are publicly available. In the course of the
pre-OmegaTranS project we identified two planet candidates - POTS-1b and
POTS-C2b - which we present in this work. With extensive follow-up observations
we were able to confirm one of them, POTS-1b, a hot Jupiter transiting a mid-K
dwarf. The planet has a mass of 2.31+-0.77M_Jup and a radius of 0.94+-0.04R_Jup
and a period of P=3.16d. The host star POTS-1 has a radius of 0.59+-0.02R_Sun
and a mass of 0.70+-0.05M_Sun. Due to its low apparent brightness of I=16.1mag
the follow-up and confirmation of POTS-1b was particularly challenging and
costly.Comment: 18 pages, 23 figures, accepted for publication in MNRA
Intermediate Resolution Near-Infrared Spectroscopy of 36 late-M Dwarfs
We present observations of 36 late-M dwarfs obtained with the KeckII/NIRSPEC
in the J-band at a resolution of \sim20,000. We have measured projected
rotational velocities, absolute radial velocities, and pseudo-equivalent widths
of atomic lines. 12 of our targets did not have previous measurements in the
literature.
For the other 24 targets, we confirm previously reported measurements. We
find that 13 stars from our sample have vsini below our measurement threshold
(12 km/s) whereas four of our targets are fast rotators (vsini > 30 km/s). As
fast rotation causes spectral features to be washed out, stars with low
projected rotational velocities are sought for radial velocity surveys.
At our intermediate spectral resolution we have confirmed the identification
of neutral atomic lines reported in Mclean et al. 2007. We also calculated
pseudo-equivalent widths (p-EW) of 12 atomic lines. Our results confirm that
the p-EW of K I lines are strongly dependent on spectral types. We observe that
the p-EW of Fe I and Mn I lines remain fairly constant with later spectral
type. We suggest that those lines are particularly suitable for deriving
metallicities for late-M dwarfs.Comment: accepted in Astronomical Journal. 30 pages, 7 tables, and 7 figure
Atomic lines in infrared spectra for ultracool dwarfs
We provide a set of atomic lines which are suitable for the description of
ultracool dwarf spectra from 10000 to 25000 \AA. This atomic linelist was made
using both synthetic spectra calculations and existing atlases of infrared
spectra of Arcturus and Sunspot umbra. We present plots, which show the
comparison of synthetic spectra and observed Arcturus and Sunspot umbral
spectra for all atomic lines likely to be observable in high resolution
infrared spectra.Comment: 21 pages, 2 tables, 129 figures, figures are available only at
http://www.astro.livjm.ac.uk/~hraj/spectralatlas/index.html, accepted to A&
Towards precise ages and masses of free floating planetary mass brown dwarfs
© 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical SocietyMeasurement of the substellar initial mass function (IMF) in very young clusters is hampered by the possibility of the age spread of clustermembers. This is particularly serious for candidate planetary mass objects (PMOs), which have a very similar location to older and more massive brown dwarfs on the Hertzsprung-Russell Diagram (HRD). This degeneracy can be lifted by the measurement of gravity-sensitive spectral features. To this end we have obtained mediumresolution (R ~ 5000) Near-infrared Integral Field Spectrometer (NIFS) K-band spectra of a sample of late M-/early L-type dwarfs. The sample comprises old field dwarfs and very young brown dwarfs in the Taurus association and in the σ Orionis cluster. We demonstrate a positive correlation between the strengths of the 2.21 μm Na I doublet and the objects' ages. We demonstrate a further correlation between these objects' ages and the shape of their K-band spectra. We have quantified this correlation in the form of a new index, the H2(K) index. This index appears to be more gravity-sensitive than the Na I doublet and has the advantage that it can be computed for spectra where gravity-sensitive spectral lines are unresolved, while it is also more sensitive to surface gravity at very young ages (<10 Myr) than the triangular H-band peak. Both correlations differentiate young objects from field dwarfs, while the H2(K) index can distinguish, at least statistically, populations of ~1Myr objects from populations of ~10 Myr objects. We applied the H2(K) index to NIFS data for one Orion nebula cluster (ONC) PMO and to previously published low-resolution spectra for several other ONC PMOs where the 2.21 μm Na I doublet was unresolved and concluded that the average age of the PMOs is ~1Myr.Peer reviewe
Infrared Mn I laboratory oscillator strengths for the study of late type stars and ultracool dwarfs
Original article can be found at: http://www.aanda.org/ Copyright The European Southern ObservatoryAims: The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs. Methods: Branching fractions have been measured by high resolution Fourier transform spectroscopy and combined with radiative level lifetimes in the literature to yield oscillator strengths. Results: We present experimental oscillator strengths for 20 transitions in the wavelength range 3216 to 13 997 Å, 15 of which are in the infrared. The transitions at 12 899 Å and 12 975 Å are observed as strong features in the spectra of late-type stars and ultracool dwarfs. We have fitted our calculated spectra to the observed lines in spectra of late-type stars. Using the new experimentally measured log(gf) values together with existing data for hyperfine structure splitting factors we determined the manganese abundance to be log N(Mn) = -6.65 ± 0.05 in the atmosphere of the Sun, log N(Mn) = 6.95 ± 0.20 in the atmosphere of Arcturus, and log N(Mn) = -6.70 ± 0.20 in the atmosphere of M 9.5 dwarf 2MASSW 0140026+270150.Peer reviewe