1,144 research outputs found
Parallaxes and Infrared Photometry of three Y0 dwarfs
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 have followed up the three Y0 dwarfs WISEPA J041022.71+150248.5, WISEPA J173835.53+273258.9 and WISEPC J205628.90+145953.3 using the UKIRT/WFCAM telescope/instruments. We find parallaxes that are more consistent and accurate than previously published values. We estimate absolute magnitudes in photometric pass-bands from to and find them to be consistent between the three Y0 dwarfs indicating the inherent cosmic absolute magnitude spread of these objects is small. We examine the MKO magnitudes over the four year time line and find small but significant monotonic variations. Finally we estimate physical parameters from a comparison of spectra and parallax to equilibrium and non-equilibrium models finding values consistent with solar metallicity, an effective temperature of 450-475\,K and log~g of 4.0-4.5.Peer reviewe
WISE Brown Dwarf Binaries: The Discovery of a T5+T5 and a T8.5+T9 System
The multiplicity properties of brown dwarfs are critical empirical constraints for formation theories, while multiples themselves provide unique opportunities to test evolutionary and atmospheric models and examine empirical trends. Studies using high-resolution imaging cannot only uncover faint companions, but they can also be used to determine dynamical masses through long-term monitoring of binary systems. We have begun a search for the coolest brown dwarfs using preliminary processing of data from the Wide-field Infrared Survey Explorer and have confirmed many of the candidates as late-type T dwarfs. In order to search for companions to these objects, we are conducting observations using the Laser Guide Star Adaptive Optics system on Keck II. Here we present the first results of that search, including a T5 binary with nearly equal mass components and a faint companion to a T8.5 dwarf with an estimated spectral type of T9
Hubble Space Telescope Spectroscopy of Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer
We present a sample of brown dwarfs identified with the {\it Wide-field
Infrared Survey Explorer} (WISE) for which we have obtained {\it Hubble Space
Telescope} ({\it HST}) Wide Field Camera 3 (WFC3) near-infrared grism
spectroscopy. The sample (twenty-two in total) was observed with the G141 grism
covering 1.101.70 m, while fifteen were also observed with the G102
grism, which covers 0.901.10 m. The additional wavelength coverage
provided by the G102 grism allows us to 1) search for spectroscopic features
predicted to emerge at low effective temperatures (e.g.\ ammonia bands) and 2)
construct a smooth spectral sequence across the T/Y boundary. We find no
evidence of absorption due to ammonia in the G102 spectra. Six of these brown
dwarfs are new discoveries, three of which are found to have spectral types of
T8 or T9. The remaining three, WISE J082507.35280548.5 (Y0.5), WISE
J120604.38840110.6 (Y0), and WISE J235402.77024015.0 (Y1) are the
nineteenth, twentieth, and twenty-first spectroscopically confirmed Y dwarfs to
date. We also present {\it HST} grism spectroscopy and reevaluate the spectral
types of five brown dwarfs for which spectral types have been determined
previously using other instruments.Comment: Accepted for publication in the Astrophysical Journal. 20 pages, 18
figures, 7 table
FIRE Spectroscopy of Five Late-type T Dwarfs Discovered with the Wide-field Infrared Survey Explorer
We present the discovery of five late-type T dwarfs identified with the
Wide-field Infrared Survey Explorer (WISE). Low-resolution near-infrared
spectroscopy obtained with the Magellan Folded-port InfraRed Echellette (FIRE)
reveal strong water and methane absorption in all five sources, and spectral
indices and comparison to spectral templates indicate classifications ranging
from T5.5 to T8.5:. The spectrum of the latest-type source, WISE J1812+2721, is
an excellent match to that of the T8.5 companion brown dwarf Wolf 940B.
WISE-based spectrophotometric distance estimates place these T dwarfs at 12-13
pc from the Sun, assuming they are single. Preliminary fits of the spectral
data to the atmosphere models of Saumon & Marley indicate effective
temperatures ranging from 600 K to 930 K, both cloudy and cloud-free
atmospheres, and a broad range of ages and masses. In particular, two sources
show evidence of both low surface gravity and cloudy atmospheres, tentatively
supporting a trend noted in other young brown dwarfs and exoplanets. In
contrast, the high proper motion T dwarf WISE J2018-7423 exhibits a suppressed
K-band peak and blue spectrophotometric J-K colors indicative of an old,
massive brown dwarf; however, it lacks the broadened Y-band peak seen in
metal-poor counterparts. These results illustrate the broad diversity of
low-temperature brown dwarfs that will be uncovered with WISE.Comment: 19 pages, 13 figures; accepted for publication to Ap
Preliminary Parallaxes of 40 L and T Dwarfs from the U.S. Naval Observatory Infrared Astrometry Program
We present preliminary trigonometric parallaxes and proper motions for 22 L
dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager. Relative to
absolute parallax corrections are made by employing 2MASS and/or SDSS
photometry for reference frame stars. We combine USNO infrared and optical
parallaxes with the best available CIT system photometry to determine M_J, M_H,
and M_K values for 37 L dwarfs between spectral types L0 to L8 and 19 T dwarfs
between spectral types T0.5 and T8 and present selected absolute magnitude
versus spectral type and color diagrams, based on these results. Luminosities
and temperatures are estimated for these objects. Of special interest are the
distances of several objects which are at or near the L-T dwarf boundary so
that this important transition can be better understood. The previously
reported early-mid T dwarf luminosity excess is clearly confirmed and found to
be present at J, H, and K. The large number of objects that populate this
luminosity excess region indicates that it cannot be due entirely to selection
effects. The T dwarf sequence is extended to M_J~16.9 by 2MASS J041519-0935
which, at d = 5.74 pc, is found to be the least luminous [log(L/L_sun)=-5.58]
and coldest (T_eff~760 K) brown dwarf known. Combining results from this paper
with earlier USNO CCD results we find that, in contrast to the L dwarfs, there
are no examples of low velocity (V_tan < 20 km/s) T dwarfs. We briefly discuss
future directions for the USNO infrared astrometry program.Comment: 73 pages, 9 figures, 9 tables, accepted for publication in The
Astronomical Journa
Secondary traumatisation and emotional exhaustion in mental healthcare providers:The mediating role of social support
Background: Burnout, especially emotional exhaustion, is common among mental healthcare providers (MHP). It is caused by exposure to prolonged stress related job conditions, such as secondary traumatisation. Social support is a protective factor for developing emotional exhaustion. In addition, higher levels of social support are associated with lower levels of secondary traumatisation. However, it is unclear how social support and secondary traumatisation are related. Social support may be a protective factor for developing secondary traumatisation, as it is for emotional exhaustion. On the other hand, MHP who suffer more from secondary traumatisation might experience less social support, for example because they fear stigmatisation. This study examined whether social support mediates the relationship between secondary traumatisation and emotional exhaustion. Further, it is explored whether the relation between secondary traumatisation and social support is moderated by profession (physicians, psychologists and case managers). Method: In total, 593 MHP participated in this cross-sectional study. Participants completed a questionnaire including demographic characteristics, secondary traumatisation, emotional exhaustion, and social support. Results: It was shown that no MHP experience high levels of secondary traumatisation and relatively few experience high levels of emotional exhaustion, while they do experience much social support. Furthermore, as hypothesized, it was found that the relationship between secondary traumatisation and emotional exhaustion is partially mediated by social support. Finally, no moderation effect of profession was found. Conclusion: These results imply that MHP have access to social support and make use of it, preventing emotional exhaustion. Mental healthcare organisations should maintain these resources for social support to prevent emotional exhaustion. MHP who are less inclined to seek social support should receive extra attention, as should MHP who are more at risk of secondary traumatisation. Even though MHP experience the availability of social support, still 25% of the MHP do experience emotional exhaustion. Future research should examine which factors for this group contribute to the development of emotional exhaustion so that appropriate measures can be taken
J-Band Infrared Spectroscopy of a Sample of Brown Dwarfs Using Nirspec on Keck II
Near-infrared spectroscopic observations of a sample of very cool, low-mass
objects are presented with higher spectral resolution than in any previous
studies. Six of the objects are L-dwarfs, ranging in spectral class from L2 to
L8/9, and the seventh is a methane or T-dwarf. These new observations were
obtained during commissioning of NIRSPEC, the first high-resolution
near-infrared cryogenic spectrograph for the Keck II 10-meter telescope on
Mauna Kea, Hawaii. Spectra with a resolving power of R=2500 from 1.135 to 1.360
microns (approximately J-band) are presented for each source. At this
resolution, a rich spectral structure is revealed, much of which is due to
blending of unresolved molecular transitions. Strong lines due to neutral
potassium (K I), and bands due to iron hydride (FeH) and steam (H2O) change
significantly throughout the L sequence. Iron hydride disappears between L5 and
L8, the steam bands deepen and the K I lines gradually become weaker but wider
due to pressure broadening. An unidentified feature occurs at 1.22 microns
which has a temperature dependence like FeH but has no counterpart in the
available FeH opacity data. Because these objects are 3-6 magnitudes brighter
in the near-infrared compared to the I-band, spectral classification is
efficient. One of the objects studied (2MASSW J1523+3014) is the coolest
L-dwarf discovered so far by the 2-Micron All-Sky Survey (2MASS), but its
spectrum is still significantly different from the methane-dominated objects
such as Gl229B or SDSS 1624+0029.Comment: New paper, Latex format, 2 figures, accepted to ApJ Letter
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