51 research outputs found
Observational m Interstellar Extinction Curves Toward Star-Forming Regions Derived from Spitzer IRS Spectra
Using \emph{Spitzer} Infrared Spectrograph observations of G0--M4 III stars
behind dark clouds, I construct m empirical extinction curves for
, which is equivalent to between 3 and 50. For
the curve appears similar to the \citet{mathis90} diffuse interstellar
medium extinction curve, but with a greater degree of extinction. For ,
the curve exhibits lower contrast between the silicate and absorption
continuum, developes ice absorption, and lies closer to the \citet{wd01}
case B curve, a result which is consistent with that of
\citet{flaherty07} and \citet{chiar07}. Recently work using \emph{Spitzer}
Infrared Array Camera data by \citet{chapman08} independently reaches a similar
conclusion, that the shape of the extinction curve changes as a function of
increasing . By calculating the optical depths of the m silicate
and 6.0, 6.8, and 15.2 m ice features, I determine that a process
involving ice is responsible for the changing shape of the extinction curve and
speculate that this process is coagulation of ice-mantled grains rather than
ice-mantled grains alone.Comment: Submitted to ApJ Letters, 5 pages, 4 figures, 1 table. Revised
version published in ApJ Letters, with 5 pages, 3 figures, and 2 tables.
Empirical extinction curves are available as online-only from Ap
The Chandra survey of the SMC "Bar": II. Optical counterparts of X-ray sources
We present the most likely optical counterparts of 113 X-ray sources detected
in our Chandra survey of the central region of the Small Magellanic Cloud (SMC)
based on the OGLE-II and MCPS catalogs. We estimate that the foreground
contamination and chance coincidence probability are minimal for the bright
optical counterparts (corresponding to OB type stars; 35 in total). We propose
here for the first time 13 High-Mass X-ray Binaries (HMXBs), of which 4 are
Be/X-ray binaries (Be-XRBs), and we confirm the previous classification of 18
Be-XRBs. We estimate that the new candidate Be-XRBs have an age of 15-85 Myr,
consistent with the age of Be stars. We also examine the "overabundance" of
Be-XRBs in the SMC fields covered by Chandra, in comparison with the Galaxy. In
luminosities down to about 10^{34} erg/s, we find that SMC Be-XRBs are 1.5
times more common when compared to the Milky Way even after taking into account
the difference in the formation rates of OB stars. This residual excess can be
attributed to the lower metallicity of the SMC. Finally, we find that the
mixing of Be-XRBs with other than their natal stellar population is not an
issue in our comparisons of Be-XRBs and stellar populations in the SMC.
Instead, we find indication for variation of the SMC XRB populations on
kiloparsec scales, related to local variations of the formation rate of OB
stars and slight variation of their age, which results in different relative
numbers of Be stars and therefore XRBs.Comment: 94 pages, 10 figures, submitted to Ap
A New Method to Identify Nearby, Young, Low-mass Stars
We describe a new method to identify young, late-type stars within ~150 pc of
the Earth that employs visual or near-infrared data and the GALEX GR4/5
database. For spectral types later than K5, we demonstrate that the ratio of
GALEX near-ultraviolet (NUV) to visual and near-IR emission is larger for stars
with ages between 10 and 100 Myr than for older, main sequence stars. A search
in regions of the sky encompassing the TW Hya and Scorpius-Centaurus
Associations has returned 54 high-quality candidates for followup.
Spectroscopic observations of 24 of these M1-M5 objects reveal Li 6708 angstrom
absorption in at least 17 systems. Because GALEX surveys have covered a
significant fraction of the sky, this methodology should prove valuable for
future young star studies.Comment: 27 pages, 8 figures, accepted for publication in ApJ. Some
significant changes were made in proof, we recommend readers use the ApJ
versio
Detection of Strong Millimeter Emission from the Circumstellar Dust Disk Around V1094 Sco: Cold and Massive Disk around a T Tauri Star in a Quiescent Accretion Phase?
We present the discovery of a cold massive dust disk around the T Tauri star
V1094 Sco in the Lupus molecular cloud from the 1.1 millimeter continuum
observations with AzTEC on ASTE. A compact (320 AU) continuum
emission coincides with the stellar position having a flux density of 272 mJy
which is largest among T Tauri stars in Lupus. We also present the detection of
molecular gas associated with the star in the five-point observations in
CO J=3--2 and CO J=3--2. Since our CO and CO
observations did not show any signature of a large-scale outflow or a massive
envelope, the compact dust emission is likely to come from a disk around the
star. The observed SED of V1094 Sco shows no distinct turnover from near
infrared to millimeter wavelengths, which can be well described by a flattened
disk for the dust component, and no clear dip feature around 10 \micron
suggestive of absence of an inner hole in the disk. We fit a simple power-law
disk model to the observed SED. The estimated disk mass ranges from 0.03 to
0.12 M_\sun, which is one or two orders of magnitude larger than the
median disk mass of T Tauri stars in Taurus.Comment: 18 pages, 4 figures, accepted for publication in Ap
Planetary Construction Zones in Occultation: Discovery of an Extrasolar Ring System Transiting a Young Sun-like Star and Future Prospects for Detecting Eclipses by Circumsecondary and Circumplanetary Disks
The large relative sizes of circumstellar and circumplanetary
disks imply that they might be seen in eclipse in stellar light curves. We
estimate that a survey of ~10^4 young (~10 Myr old) post-accretion pre-MS stars
monitored for ~10 years should yield at least a few deep eclipses from
circumplanetary disks and disks surrounding low mass companion stars. We
present photometric and spectroscopic data for a pre-MS K5 star (1SWASP
J140747.93-394542.6), a newly discovered ~0.9 Msun member of the ~16 Myr-old
Upper Cen-Lup subgroup of Sco-Cen at a kinematic distance of 128 pc. SuperWASP
and ASAS light curves for this star show a remarkably long, deep, and complex
eclipse event centered on 29 April 2007. At least 5 multi-day dimming events of
>0.5 mag are identified, with a >3.3 mag deep eclipse bracketed by two pairs of
~1 mag eclipses symmetrically occurring +-12 days and +-26 days before and
after. Hence, significant dimming of the star was taking place on and off over
at least a ~54 day period in 2007, and a strong >1 mag dimming event occurred
over a ~12 day span. We place a firm lower limit on the period of 850 days
(i.e. the orbital radius of the eclipser must be >1.7 AU and orbital velocity
must be <22 km/s). The shape of the light curve is similar to the lop-sided
eclipses of the Be star EE Cep. We suspect that this new star is being eclipsed
by a low-mass object orbited by a dense inner disk, girded by at least 3 dusty
rings of lower optical depth. Between these rings are at least two annuli of
near-zero optical depth (i.e. gaps), possibly cleared out by planets or moons,
depending on the nature of the secondary. For possible periods in the range
2.33-200 yr, the estimated total ring mass is ~8-0.4 Mmoon (if the rings have
optical opacity similar to Saturn's rings), and the edge of the outermost
detected ring has orbital radius ~0.4-0.09 AU.Comment: Astronomical Journal, in press, 13 figure
OGLE-II High Proper Motion Stars towards the Galactic centre
The photometry data base of the second phase of the OGLE microlensing
experiment, OGLE-II, is a rich source of information about the kinematics and
structure of the Galaxy. In this work we use the OGLE-II proper motion
catalogue to identify candidate stars which have high proper motions. 521 stars
with proper motion mu > 50 mas/yr in the OGLE-II proper motion catalogue (Sumi
2004) were cross-identified with stars in the MACHO high proper motion
catalogue, and the DENIS and 2MASS infra-red photometry catalogues. Photometric
distances were computed for stars with colours consistent with G/K and M type
stars. 6 stars were newly identified as possible nearby (< 50 pc) M dwarfs.Comment: 7 figures and 4 tables, MNRAS, accepte
The Solar Neighborhood XXIII CCD Photometric Distance Estimates of SCR Targets -- 77 M Dwarf Systems within 25 Parsecs
We present CCD photometric distance estimates of 100 SCR (SuperCOSMOS RECONS)
systems with 0\farcs18/yr, 28 of which are new discoveries
previously unpublished in this series of papers. These distances are estimated
using a combination of new photometry acquired at CTIO and
magnitudes extracted from 2MASS. The estimates are improvements over those
determined using photographic plate magnitudes from SuperCOSMOS plus
, as presented in the original discovery papers. In total, 77 of the 100
systems investigated are predicted to be within 25 pc. If all 77 systems are
confirmed to have 40 milliarcseconds, this sample would
represent a 23% increase in M dwarf systems nearer than 25 pc in the southern
sky.Comment: 34 pages, 8 figure
UBV(RI)_C photometry of transiting planet host stars
We present new UBV(RI)_C photometry of 22 stars that host transiting planets,
19 of which were discovered by the WASP survey. We use these data together with
2MASS JHK_S photometry to estimate the effective temperature of these stars
using the infrared flux method. We find that the effective temperature
estimates for stars discovered by the WASP survey based on the analysis of
spectra are reliable to better than their quoted uncertainties.Comment: Accepted for publication in MNRAS. 4 pages, 1 figur
Recommendations from the European Working Group for Value Assessment and Funding Processes in Rare Diseases (ORPH-VAL)
International audienceAbstractRare diseases are an important public health issue with high unmet need. The introduction of the EU Regulation on orphan medicinal products (OMP) has been successful in stimulating investment in the research and development of OMPs. Despite this advancement, patients do not have universal access to these new medicines. There are many factors that affect OMP uptake, but one of the most important is the difficulty of making pricing and reimbursement (P&R) decisions in rare diseases. Until now, there has been little consensus on the most appropriate assessment criteria, perspective or appraisal process. This paper proposes nine principles to help improve the consistency of OMP P&R assessment in Europe and ensure that value assessment, pricing and funding processes reflect the specificities of rare diseases and contribute to both the sustainability of healthcare systems and the sustainability of innovation in this field. These recommendations are the output of the European Working Group for Value Assessment and Funding Processes in Rare Diseases (ORPH-VAL), a collaboration between rare disease experts, patient representatives, academics, health technology assessment (HTA) practitioners, politicians and industry representatives. ORPH-VAL reached its recommendations through careful consideration of existing OMP P&R literature and through a wide consultation with expert stakeholders, including payers, regulators and patients. The principles cover four areas: OMP decision criteria, OMP decision process, OMP sustainable funding systems and European co-ordination. This paper also presents a guide to the core elements of value relevant to OMPs that should be consistently considered in all OMP appraisals. The principles outlined in this paper may be helpful in drawing together an emerging consensus on this topic and identifying areas where consistency in payer approach could be achievable and beneficial. All stakeholders have an obligation to work together to ensure that the promise of OMP’s is realised
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