699 research outputs found
Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey - II. The Alpha Persei open cluster
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present the results of a deep (J = 19.1mag) infrared (ZYJHK) survey over the full α Per open cluster extracted from the Data Release 9 of the United Kingdom Infrared Telescope Infrared Deep Sky Survey Galactic Clusters Survey (UKIDSS). We have selected ∼700 cluster member candidates in ∼56 square degrees in α Per by combining photometry in five near-infrared passbands and proper motions derived from the multiple epochs provided by the UKIDSS Galactic Clusters Survey (GCS) Data Release 9 (DR9). We also provide revised membership for all previously published α Per low-mass stars and brown dwarfs recovered in GCS based on the new photometry and astrometry provided by DR9. We find no evidence of K-band variability in members of α Per with dispersion less than 0.06-0.09mag. We employed two independent but complementary methods to derive the cluster luminosity and mass functions: a probabilistic analysis and a more standard approach consisting of stricter astrometric and photometric cuts. We find that the resulting luminosity and mass functions obtained from both methods are consistent. We find that the shape of the α Per mass function is similar to that of the Pleiades although the characteristic mass may be higher after including higher mass data from earlier studies (the dispersion is comparable). We conclude that the mass functions of α Per, the Pleiades and Praesepe are best reproduced by a log-normal representation similar to the system field mass function although with some variation in the characteristic mass and dispersion values.Peer reviewe
A New Ultracool White Dwarf Discovered in the SuperCOSMOS Sky Survey
We present photographic B, R and I photometry, and optical and near-infrared
spectroscopy, of a new ultracool white dwarf (UCWD) discovered in the
SuperCOSMOS Sky Survey. The spectrum of SSSJ1556-0806 shows strong flux
suppression due to the presence of collisionally induced absorption by
molecular hydrogen (H2CIA), a feature characteristic of the cool, high density
environments found in the atmospheres of ultracool white dwarfs. SSSJ1556-0806
therefore joins a list of <10 ultracool white dwarfs displaying extreme flux
suppression. Synthetic model fitting suggests an effective temperature <3000K,
which if true would make this one of the coolest white dwarfs currently known.
We also exploit the similarity between the SEDs of SSSJ1556-0806 and the
well-studied UCWD LHS 3250 to aid in the determination of the atmospheric
parameters in a regime where models consistently fail to reproduce
observations. SSSJ1556-0806 is relatively bright (R ~ 17.8), making it
particularly amenable to follow up observations to obtain trigonometric
parallax and IR photometry.Comment: Accepted for publication in MNRA
Cleaning sky survey databases using Hough Transform and Renewal String approaches
Large astronomical databases obtained from sky surveys such as the
SuperCOSMOS Sky Survey (SSS) invariably suffer from spurious records coming
from artefactual effects of the telescope, satellites and junk objects in orbit
around earth and physical defects on the photographic plate or CCD. Though
relatively small in number these spurious records present a significant problem
in many situations where they can become a large proportion of the records
potentially of interest to a given astronomer. Accurate and robust techniques
are needed for locating and flagging such spurious objects, and we are
undertaking a programme investigating the use of machine learning techniques in
this context. In this paper we focus on the four most common causes of unwanted
records in the SSS: satellite or aeroplane tracks, scratches, fibres and other
linear phenomena introduced to the plate, circular halos around bright stars
due to internal reflections within the telescope and diffraction spikes near to
bright stars. Appropriate techniques are developed for the detection of each of
these. The methods are applied to the SSS data to develop a dataset of spurious
object detections, along with confidence measures, which can allow these
unwanted data to be removed from consideration. These methods are general and
can be adapted to other astronomical survey data.Comment: Accepted for MNRAS. 17 pages, latex2e, uses mn2e.bst, mn2e.cls,
md706.bbl, shortbold.sty (all included). All figures included here as low
resolution jpegs. A version of this paper including the figures can be
downloaded from http://www.anc.ed.ac.uk/~amos/publications.html and more
details on this project can be found at
http://www.anc.ed.ac.uk/~amos/sattrackres.htm
Southern Infrared Proper Motion Survey I: Discovery of New High Proper Motion Stars From First Full Hemisphere Scan
We present the first results from the Southern Infrared Proper Motion Survey.
Using 2 Micron All Sky Survey data along with that of the SuperCOSMOS sky
survey we have been able to produce the first widefield infrared proper motion
survey. Having targeted the survey to identify nearby M, L and T dwarfs we have
discovered 72 such new objects with proper motions greater than 0.5''/yr with
10 of these having proper motions in excess of 1''/yr. The most interesting of
these objects is SIPS1259-4336 a late M dwarf. We have calculated a
trigonometric parallax for this object of milliarcseconds
yielding a distance of pc. We have also discovered a common proper
motion triple system and an object with a common proper motion with LHS 128.
The survey completeness is limited by the small epoch differences between many
2MASS and UKI observations. Hence we only recover 22% of Luyten objects with
favourable photometry. However the Luyten study is itself unquantifiably
incomplete. We discuss the prospect of enhancing the survey volume by reducing
the lower proper motion limit.Comment: 20 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
The Solar Neighborhood VIII: Discovery of New High Proper Motion Nearby Stars Using the SuperCOSMOS Sky Survey
Five new objects with proper motions between 1.0 arcsec/yr and 2.6 arcsec/yr
have been discovered via a new RECONS search for high proper motion stars
utilizing the SuperCOSMOS Sky Survey. The first portion of the search,
discussed here, is centered on the south celestial pole and covers declinations
-90 degrees to -57.5 degrees.
Photographic photometry from SuperCOSMOS and JHKs near-infrared photometry
from 2MASS for stars nearer than 10 pc are combined to provide a suite of new
M_Ks-color relations useful for estimating distances to main sequence stars.
These relations are then used to derive distances to the new proper motion
objects as well as previously known stars with mu >= 1.0 arcsec/yr (many of
which have no trigonometric parallaxes) recovered during this phase of the
survey.
Four of the five new stars have red dwarf colors, while one is a nearby white
dwarf. Two of the red dwarfs are likely to be within the RECONS 10 pc sample,
and the white dwarf probably lies between 15 and 25 pc. Among the 23 known
stars recovered during the search, there are three additional candidates for
the RECONS sample that have no trigonometric parallaxes.Comment: 17 pages, 5 figures; accepted for publication in Astronomy Journa
Optical spectroscopy of candidate Alpha Persei white dwarfs
As part of an investigation into the high mass end of the initial mass-final
mass relation we performed a search for new white dwarf members of the nearby
(172.4 pc), young (80-90 Myr) Persei open star cluster. The
photometric and astrometric search using the UKIRT Infrared Deep Sky Survey and
SuperCOSMOS sky surveys discovered 14 new white dwarf candidates. We have
obtained medium resolution optical spectra of the brightest 11 candidates using
the William Herschel Telescope and confirmed that while 7 are DA white dwarfs,
3 are DB white dwarfs and one is an sdOB star, only three have cooling ages
within the cluster age, and from their position on the initial mass-final mass
relation, it is likely none are cluster members. This result is disappointing,
as recent work on the cluster mass function suggests that there should be at
least one white dwarf member, even at this young age. It may be that any white
dwarf members of Per are hidden within binary systems, as is the case
in the Hyades cluster, however the lack of high mass stars within the cluster
also makes this seem unlikely. One alternative is that a significant level of
detection incompleteness in the legacy optical image survey data at this
Galactic latitude has caused some white dwarf members to be overlooked. If this
is the case, Gaia will find them.Comment: 8 pages, 7 Figures, 3 Tables. Accepted for publication in MNRA
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