50 research outputs found
A blue depression in the optical spectra of M dwarfs
A blue depression is found in the spectra of M dwarfs from 4000 to 4500A.
This depression shows an increase toward lower temperatures though is
particularly sensitive to gravity and metallicity. It is the single most
sensitive feature in the optical spectra of M dwarfs. The depression appears as
centered on the neutral calcium resonance line at 4227A and leads to nearby
features being weaker by about two orders of magnitude than predicted. We
consider a variety of possible causes for the depression including temperature,
gravity, metallicity, dust, damping constants, and atmospheric stratification.
We also consider relevant molecular opacities which might be the cause
identifying AlH, SiH, and NaH in the spectral region. However, none of these
solutions are satisfactory. In the absence of a more accurate determination of
the broadening of the calcium line perturbed by molecular hydrogen, we find a
promising empirical fit using a modified Lorentzian line profile for the
calcium resonance line. Such fits provide a simplistic line-broadening
description for this calcium resonance line and potentially other un-modelled
resonance lines in cool high-pressure atmospheres. Thus we claim the most
plausible cause of the blue depression in the optical spectra of M dwarfs is a
lack of appropriate treatment of line broadening for atomic calcium. The broad
wings of the calcium resonance line develop at temperatures below about 4000K
and are analogous to the neutral sodium and potassium features which dominate
the red optical spectra of L dwarfs.Comment: Accepted in MNRA
The metal rich abundance pattern - spectroscopic properties and abundances for 107 main-sequence stars
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, ©: 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We report results from the high resolution spectral analysis of the 107 metal rich (mostly [Fe/H]7.67 dex) target stars from the Calan-Hertfordshire Extrasolar Planet Search program observed with HARPS. Using our procedure of finding the best fit to the absorption line profiles in the observed spectra, we measure the abundances of Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zn, and we then compare them with known results from different authors. Most of our abundances agree with these works at the level of 0.05 dex or better for the stars we have in common. However, we do find systematic differences that make direct inferences difficult. Our analysis suggests that the selection of line lists and atomic line data along with the adopted continuum level influence these differences the most. At the same time, we confirm the positive trends of abundances versus metallicity for Na, Mn, Ni, and to a lesser degree, Al. A slight negative trend is observed for Ca, whereas Si and Cr tend to follow iron. Our analysis allows us to determine the positively skewed normal distribution of projected rotational velocities with a maximum peaking at 3 km s. Finally, we obtained a Gaussian distribution of microturbulent velocities that has a maximum at 1.2 km s and a full width at half maximum 0.35 km s, indicating that metal rich dwarfs and subgiants in our sample have a very restricted range in microturbulent velocity.Peer reviewedFinal Published versio
Identifying and characterizing ultracool dwarfs ejected from post-encounter disintegrating systems
Disintegrating multiple systems have been previously discovered from
kinematic studies of the catalogue. They are presumably the
result of dynamical encounters taking place in the Galactic disk between
single/multiple systems. In this paper, we aim to expand the search for such
systems, to study their properties, as well as to characterize possible
low-mass ejecta (i.e. brown dwarfs and planets). We have assembled a list of 15
candidate systems using astrometry from the Tycho-Gaia astrometric solution
(later upgraded with DR3), and here we present the discovery and
follow-up of 5 of them. We have obtained DECam imaging for all 5 systems and by
combining near-infrared photometry and proper motion, we searched for
ultra-cool ejected components. We find that the system consisting of TYC
7731-1951-1, TYC 7731-2128 AB, and TYC 7731-1995-1ABC?, contains one very
promising ultra-cool dwarf candidate. Using additional data from the
literature, we have found that 3 out of 5 disintegrating system candidates are
likely to be true disintegrating systems.Comment: Accepted for publication in MNRAS. 17 pages, 8 figures, 4 table
The Transit Light Curve Project. VII. The Not-So-Bloated Exoplanet HAT-P-1b
We present photometry of the G0 star HAT-P-1 during six transits of its
close-in giant planet, and we refine the estimates of the system parameters.
Relative to Jupiter's properties, HAT-P-1b is 1.20 +/- 0.05 times larger and
its surface gravity is 2.7 +/- 0.2 times weaker. Although it remains the case
that HAT-P-1b is among the least dense of the known sample of transiting
exoplanets, its properties are in accord with previously published models of
strongly irradiated, coreless, solar-composition giant planets. The times of
the transits have a typical accuracy of 1 min and do not depart significantly
from a constant period.Comment: To appear in AJ [19pg, 3 figures]. New co-author added. Minor
revisions to match published versio
The observed distribution of spectroscopic binaries from the Anglo-Australian Planet Search
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We report the detection of sixteen binary systems from the Anglo-Australian Planet Search. Solutions to the radial velocity data indicate that the stars have companions orbiting with a wide range of masses, eccentricities and periods. Three of the systems potentially contain brown-dwarf companions while another two have eccentricities that place them in the extreme upper tail of the eccentricity distribution for binaries with periods less than 1000 d. For periods up to 12 years, the distribution of our stellar companion masses is fairly flat, mirroring that seen in other radial velocity surveys, and contrasts sharply with the current distribution of candidate planetary masses, which rises strongly below 10 MJ. When looking at a larger sample of binaries that have FGK star primaries as a function of the primary star metallicity, we find that the distribution maintains a binary fraction of ∼43 ± 4 per cent between −1.0 and +0.6 dex in metallicity. This is in stark contrast to the giant exoplanet distribution. This result is in good agreement with binary formation models that invoke fragmentation of a collapsing giant molecular cloud, suggesting that this is the dominant formation mechanism for close binaries and not fragmentation of the primary star's remnant protoplanetary disc.Peer reviewe
Precision radial velocities of 15 M5-M9 dwarfs
J. R. Barnes, 'Precision radial velocities of 15 M5-M9 dwarfs', Monthly Notices of the Royal Astronomical Society, Vol. 439 (3): 3094 - 3113, first published online 20 February 2014. The version of record is available online at doi: 10.1093/mnras/stu172 © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We present radial velocity measurements of a sample ofM5V-M9Vstars from our Red-Optical Planet Survey, operating at 0.652-1.025 μm. Radial velocities for 15 stars, with rms precision down to 2.5m-1 over a week-long time-scale, are achieved using thorium-argon reference spectra. We are sensitive to planets with mp sin i ≥ 1.5M⊕ (3M⊕ at 2σ) in the classical habitable zone, and our observations currently rule out planets with mp sini ≥ 0.5MJ at 0.03 au for all our targets. A total of 9 of the 15 targets exhibit rms 10M⊕ in 0.03 au orbits. Since the mean rotation velocity is of the order of 8 km-1 for an M6V star and 15 km -1 for M9V, we avoid observing only slow rotators that would introduce a bias towards low axial inclination (i< 90°) systems, which are unfavourable for planet detection. Our targets with the highest v sin i values exhibit radial velocities significantly above the photon-noise-limited precision, even after accounting for v sin i. We have therefore monitored stellar activity via chromospheric emission from the Hα and Ca II infrared triplet lines. A clear trend of log10(LHα/Lbol) with radial velocity rms is seen, implying that significant starspot activity is responsible for the observed radial velocity precision floor. The implication that most late M dwarfs are significantly spotted, and hence exhibit time varying line distortions, indicates that observations to detect orbiting planets need strategies to reliablymitigate against the effects of activity-induced radial velocity variations.Peer reviewe
The Calan-Hertfordshire Extrasolar Planet Search
The detailed study of the exoplanetary systems HD189733 and HD209458 has
given rise to a wealth of exciting information on the physics of exoplanetary
atmospheres. To further our understanding of the make-up and processes within
these atmospheres we require a larger sample of bright transiting planets. We
have began a project to detect more bright transiting planets in the southern
hemisphere by utilising precision radial-velocity measurements. We have
observed a constrained sample of bright, inactive and metal-rich stars using
the HARPS instrument and here we present the current status of this project,
along with our first discoveries which include a brown dwarf/extreme-Jovian
exoplanet found in the brown dwarf desert region around the star HD191760 and
improved orbits for three other exoplanetary systems HD48265, HD143361 and
HD154672. Finally, we briefly discuss the future of this project and the
current prospects we have for discovering more bright transiting planets.Comment: 4 pages, 2 figures, to appear in the conference proceedings "New
Technologies for Probing the Diversity of Brown Dwarfs and Exoplanets"
Shanghai 200
Anomalous small angle x-ray scattering simulations: proof of concept for distance measurements for nanoparticle-labelled biomacromolecules in solution.
Anomalous small angle X-ray scattering can in principle be used to determine distances between metal label species on biological molecules. Previous experimental studies in the past were unable to distinguish the label-label scattering contribution from that of the molecule, because of the use of atomic labels; these labels contribute only a small proportion of the total scattering signal. However, with the development of nanocrystal labels (of 50-100 atoms) there is the possibility for a renewed attempt at applying anomalous small angle X-ray scattering for distance measurement. This is because the contribution to the scattered signal is necessarily considerably stronger than for atomic labels. Here we demonstrate through simulations, the feasibility of the technique to determine the end-to-end distances of labelled nucleic acid molecules as well as other internal distances mimicking a labelled DNA binding protein if the labels are dissimilar metal nanocrystals. Of crucial importance is the ratio of mass of the nanocrystals to that of the labelled macromolecule, as well as the level of statistical errors in the scattering intensity measurements. The mathematics behind the distance determination process is presented, along with a fitting routine than incorporates maximum entropy regularisation