157 research outputs found
Near-infrared spectra of ISO selected Chamaeleon I young stellar objects
We present 0.95--2.5 micron moderate (R = 500) resolution spectra of 19
ISOCAM detected sources in the Chamaeleon I dark cloud. Thirteen of these stars
are candidate very low mass members of the cloud proposed by Persi et al. (2000
A&A 357:219) on basis of the mid-IR color excess. The sample also includes a
bona-fide young brown dwarf (Cha Halpha 1), a transition
--stellar/sub-stellar-- object (Cha Halpha 2), one previously known T Tauri
star (Sz 33) and three ISOCAM sources with no mid-IR excess. The spectra of the
mid-IR color excess sources are relatively flat and featureless in this
wavelength range. Both atomic and molecular lines (when in absorption) are
partially veiled suggesting the presence of continuum emission from
circumstellar dust. In addition some of the sources show Paschen and Brackett
lines in emission. We apply the 2 micron water vapor index defined by Wilking
et al. (1999 AJ 117:469) to estimate spectral types. These stars have spectral
types M0--8. We use Persi et al.'s stellar luminosity determinations, in
combination with D'Antona & Mazzitelli latest pre-main sequence evolutionary
tracks, to estimate masses and ages. The ISOCAM detected mid-IR excess sources
have sub-solar masses down to the H-burning limit and a median age of few x
10^6 yr, in good agreement with the higher mass members of this cloud.Comment: Preprint in Manuscript format; 30 pages including 10 figure
FU Orionis resolved by infrared long baseline interferometry at a 2-AU scale
We present the first infrared interferometric observations of a young stellar
object with a spatial projected resolution better than 2 AU. The observations
were obtained with the Palomar Testbed Interferometer. FU Ori exhibits a
visibility of V^2 =0.72 +/- 0.07 for a 103 +/- 5 m projected baseline at lambda
= 2.2 microns. The data are consistent on the spatial scale probed by PTI both
with a binary system scenario (maximum magnitude difference of 2.7 +/- 0.5 mag
and smallest separation of 0.35 +/- 0.05 AU) and a standard luminous accretion
disk model (approx. accretion rate of 6e-5 Mo/yr) where the thermal emission
dominates the stellar scattering, and inconsistent with a single stellar
photosphere.Comment: 13 pages, 4 figures, accepted for publication in ApJ
Near-infrared integral-field spectra of the planet/brown dwarf companion AB Pic b
Chauvin et al. 2005 imaged a co-moving companion at ~260 AU from the young
star AB Pic A. Evolutionary models predictions based on J H K photometry of AB
Pic b suggested a mass of ~13 - 14 MJup, placing the object at the
deuterium-burning boundary. We used the adaptive-optics-fed integral field
spectrograph SINFONI to obtain high quality medium-resolution spectra of AB Pic
b (R = 1500-2000) over the 1.1 - 2.5 microns range. Our analysis relies on the
comparison of our spectra to young standard templates and to the latest
libraries of synthetic spectra developed by the Lyon's Group. AB Pic b is
confirmed to be a young early-L dwarf companion. We derive a spectral type
L0-L1 and find several features indicative of intermediate gravity atmosphere.
A comparison to synthetic spectra yields Teff = 2000+100-300 K and log(g) = 4
+- 0.5 dex. The determination of the derived atmospheric parameters of AB Pic b
is limited by a non-perfect match of current atmosphere spectra with our
near-infrared observations of AB Pic b. The current treatment of dust settling
and missing molecular opacity lines in the atmosphere models could be
responsible. By combining the observed photometry, the surface fluxes from
atmosphere models and the known distance of the system, we derive new mass,
luminosity and radius estimates of AB Pic b. They confirm independently the
evolutionary model predictions. We finally review the current methods used to
characterize planetary mass companions and discuss them in the perspective of
future planet deep imaging surveys.Comment: 8 pages, 8 figure
The Palomar Testbed Interferometer
The Palomar Testbed Interferometer (PTI) is a long-baseline infrared
interferometer located at Palomar Observatory, California. It was built as a
testbed for interferometric techniques applicable to the Keck Interferometer.
First fringes were obtained in July 1995. PTI implements a dual-star
architecture, tracking two stars simultaneously for phase referencing and
narrow-angle astrometry. The three fixed 40-cm apertures can be combined
pair-wise to provide baselines to 110 m. The interferometer actively tracks the
white-light fringe using an array detector at 2.2 um and active delay lines
with a range of +/- 38 m. Laser metrology of the delay lines allows for servo
control, and laser metrology of the complete optical path enables narrow-angle
astrometric measurements. The instrument is highly automated, using a
multiprocessing computer system for instrument control and sequencing.Comment: ApJ in Press (Jan 99) Fig 1 available from
http://huey.jpl.nasa.gov/~bode/ptiPicture.html, revised duging copy edi
Palomar Testbed Interferometer
The Palomar Testbed Interferometer (PTI) is an infrared, phase-tracking interferometer in operation at Palomar Mountain since July 1995. It was funded by NASA for the purpose of developing techniques and methodologies for doing narrowangle astrometry for the purpose of detecting extrasolar planets. The instrument employs active fringe trackingin the infrared (2.0-2.4 μm) to monitor fringe phase. It is a dual-star interferometer; it is able to measure fringes on two separate stars simultaneously. An end-to-end heterodyne laser metrology system is used to monitor the optical path length of the starlight. Recently completed engineering upgrades have improved the initial instrument performance. These upgrades are:extended wavelength coverage, a single mode fiber for spatial filtering, vacuum pipes to relay the beams, accelerometers on the siderostat mirrors and a new baseline. Results of recent astrometry data indicate the instrument is approaching the astrometric limit as set by the atmosphere
Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared
We present a possible interpretation for the increase of the angular diameter
of the Mira variables o Cet, R Leo, and chi Cyg from the K band to the 11
micron region revealed by the recent interferometric observations using narrow
bandpasses where no salient spectral feature is present (Weiner et al. 2003a,
2003b). A simple two-layer model consisting of hot and cool H2O layers for the
warm water vapor envelope can reproduce the angular diameters observed with
Infrared Spatial Interferometer as well as the high-resolution TEXES spectra
obtained in the 11 micron region. The strong absorption of H2O expected from
the dense water vapor envelope is filled in by emission from the extended part
of the envelope, and this results in the high-resolution 11 micron spectra
which exhibit only weak, fine spectral features, masking the spectroscopic
evidences of the dense, warm water vapor envelope. On the other hand, the
presence of the warm water vapor envelope manifests itself as the larger
angular diameters in the 11 micron region as compared to those measured in the
near-infrared. Furthermore, comparison of the visibilities predicted in the
near-infrared with observational results available in the literature
demonstrates that our two-layer model for the warm water vapor envelope can
also reproduce the observed near-infrared visibilities and angular diameters.
The radii of the hot H2O layers in the three Mira variables are derived to be
1.5--1.7 Rstar with temperatures of 1800--2000 K and H2O column densities of
(1--5) x 10^{21} cm^{-2}, while the radii of the cool H2O layers are derived to
be 2.2--2.5 Rstar with temperatures of 1200--1400 K and H2O column densities of
(1--7) x 10^{21} cm^{-2}.Comment: 15 pages, 17 figures, accepted for publication in A&
Environmental controls on benthic food web functions and carbon resource use in subarctic lakes
Climate warming and consequent greening of subarctic landscapes increase the availability of organic carbon to the detrital food webs in aquatic ecosystems. This may cause important shifts in ecosystem functioning through the functional feeding patterns of benthic organisms that rely differently on climatically altered carbon resources. Twenty-five subarctic lakes in Finnish Lapland across a tree line ecotone were analysed for limnological and optical variables, carbon (delta C-13) and nitrogen (delta N-15) stable isotope (SI) composition of surface sediment organic matter (OM) and fossil Chironomidae (Diptera) remains to examine environmental controls behind chironomid functional feeding group (FFG) structure and their isotopic associations for assessing ecosystem functioning and carbon utilisation. We hypothesise that the chironomid SI signatures reflect increased allochthony with increasing allochthonous input, but the resource use may be altered by the functional characteristics of the assemblage. Multivariate analyses indicated that carbon geochemistry in the sediments (delta C-13, delta N-15, C/N), nutrients, indices of productivity (chlorophyll-a) and lake water optical properties, related to increasing presence of OM, played a key role in defining the chironomid FFG composition and isotopic signatures. Response modelling was used to examine how individual FFGs respond to environmental gradients. They showed divergent responses for OM quantity, dissolved organic carbon and nutrients between feeding strategies, suggesting that detritivores and filter feeders prefer contrasting carbon and nutrient conditions, and may thus hold paleoecological indicator potential to identify changes between different carbon fluxes. Benthic production was the primary carbon source for the chironomid assemblages according to a three-source SI mixing model, whereas pelagic and terrestrial components contributed less. Between-lake variability in source utilisation was high and controlled primarily by allochthonous OM inputs. Combination of biogeochemical modelling and functional classification is useful to widen our understanding of subarctic lake ecosystem functions and responses to climate-driven changes in limnology and catchment characteristics for long-term environmental change assessments and functional paleoecology.Peer reviewe
The near-infrared size-luminosity relations for Herbig Ae/Be disks
We report the results of a sensitive K-band survey of Herbig Ae/Be disk sizes
using the 85-m baseline Keck Interferometer. Targets were chosen to span the
maximum range of stellar properties to probe the disk size dependence on
luminosity and effective temperature. For most targets, the measured
near-infrared sizes (ranging from 0.2 to 4 AU) support a simple disk model
possessing a central optically-thin (dust-free) cavity, ringed by hot dust
emitting at the expected sublimation temperatures (T_sub~1000-1500K).
Furthermore, we find a tight correlation of disk size with source luminosity R
propto L^(1/2) for Ae and late Be systems (valid over more than 2 decades in
luminosity), confirming earlier suggestions based on lower-quality data.
Interestingly, the inferred dust-free inner cavities of the highest luminosity
sources (Herbig B0-B3 stars) are under-sized compared to predictions of the
optically-thin cavity model, likely due to optically-thick gas within the inner
AU.Comment: Accepted by Astrophysical Journal; 24 pages, 4 figures, 4 table
The Visual Orbit of 64 Piscum
We report on the determination of the visual orbit of the double-lined
spectroscopic binary system 64 Piscum with data obtained by the Palomar Testbed
Interferometer in 1997 and 1998. 64 Psc is a nearly equal-mass double-lined
binary system whose spectroscopic orbit is well known. We have estimated the
visual orbit of 64 Psc from our interferometric visibility data. Our 64 Psc
orbit is in good agreement with the spectroscopic results, and the physical
parameters implied by a combined fit to our interferometric visibility data and
radial velocity data of Duquennoy and Mayor result in precise component masses
that agree well with their spectral type identifications. In particular, the
orbital parallax of the system is determined to be 43.29 \pm 0.46 mas, and
masses of the two components are determined to be 1.223 \pm 0.021 M_{\sun} and
1.170 \pm 0.018 M_{\sun}, respectively.
Nadal et al. put forward arguments of temporal variability in some of the
orbital elements of 64 Psc, presumably explained by an undetected component in
the system. While our visibility data does not favor the Nadal temporal
variability inference, neither is it definitive in excluding it. Consequently
we have performed both high dynamic-range near-infrared imaging and
spectroscopy of potential additional companions to the 64 Psc system. Our
imaging and spectroscopic data do not support the conjecture of an additional
component to 64 Psc, but we did identify a faint object with unusual red colors
and spectra.Comment: ApJ In Pres
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