335 research outputs found
Strong Near-Infrared Emission Interior to the Dust-Sublimation Radius of Young Stellar Objects MWC275 and AB Aur
Using the longest optical-interferometeric baselines currently available, we
have detected strong near-infrared (NIR) emission from inside the
dust-destruction radius of Herbig Ae stars MWC275 and AB Aur. Our
sub-milli-arcsecond resolution observations unambiguously place the emission
between the dust-destruction radius and the magnetospheric co-rotation radius.
We argue that this new component corresponds to hot gas inside the
dust-sublimation radius, confirming recent claims based on spectrally-resolved
interferometry and dust evaporation front modeling.Comment: 12 pages, 4 figures, Accepted for publication in ApJ
Imaging the asymmetric dust shell around CI Cam with long baseline optical interferometry
We present the first high angular resolution observation of the B[e]
star/X-ray transient object CI Cam, performed with the two-telescope Infrared
Optical Telescope Array (IOTA), its upgraded three-telescope version (IOTA3T)
and the Palomar Testbed Interferometer (PTI). Visibilities and closure phases
were obtained using the IONIC-3 integrated optics beam combiner. CI Cam was
observed in the near-infrared H and K spectral bands, wavelengths well suited
to measure the size and study the geometry of the hot dust surrounding CI Cam.
The analysis of the visibility data over an 8 year period from soon after the
1998 outburst to 2006 shows that the dust visibility has not changed over the
years. The visibility data shows that CI Cam is elongated which confirms the
disc-shape of the circumstellar environment and totally rules out the
hypothesis of a spherical dust shell. Closure phase measurements show direct
evidence of asymmetries in the circumstellar environment of CI Cam and we
conclude that the dust surrounding CI Cam lies in an inhomogeneous disc seen at
an angle. The near-infrared dust emission appears as an elliptical skewed
Gaussian ring with a major axis a = 7.58 +/- 0.24 mas, an axis ratio r = 0.39
+/- 0.03 and a position angle theta = 35 +/- 2 deg.Comment: 9 pages, 5 figures, accepted MNRA
Imaging the spotty surface of Betelgeuse in the H band
This paper reports on H-band interferometric observations of Betelgeuse made
at the three-telescope interferometer IOTA. We image Betelgeuse and its
asymmetries to understand the spatial variation of the photosphere, including
its diameter, limb darkening, effective temperature, surrounding brightness,
and bright (or dark) star spots. We used different theoretical simulations of
the photosphere and dusty environment to model the visibility data. We made
images with parametric modeling and two image reconstruction algorithms: MIRA
and WISARD. We measure an average limb-darkened diameter of 44.28 +/- 0.15 mas
with linear and quadratic models and a Rosseland diameter of 45.03 +/- 0.12 mas
with a MARCS model. These measurements lead us to derive an updated effective
temperature of 3600 +/- 66 K. We detect a fully-resolved environment to which
the silicate dust shell is likely to contribute. By using two imaging
reconstruction algorithms, we unveiled two bright spots on the surface of
Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5%
of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of
the total flux. Resolved images of Betelgeuse in the H band are asymmetric at
the level of a few percent. The MOLsphere is not detected in this wavelength
range. The amount of measured limb-darkening is in good agreement with model
predictions. The two spots imaged at the surface of the star are potential
signatures of convective cells.Comment: 10 pages, 10 figures, accepted for publication in A&A, references
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Runx2 transcriptome of prostate cancer cells: insights into invasiveness and bone metastasis
<p>Abstract</p> <p>Background</p> <p>Prostate cancer (PCa) cells preferentially metastasize to bone at least in part by acquiring osteomimetic properties. Runx2, an osteoblast master transcription factor, is aberrantly expressed in PCa cells, and promotes their metastatic phenotype. The transcriptional programs regulated by Runx2 have been extensively studied during osteoblastogenesis, where it activates or represses target genes in a context-dependent manner. However, little is known about the gene regulatory networks influenced by Runx2 in PCa cells. We therefore investigated genome wide mRNA expression changes in PCa cells in response to Runx2.</p> <p>Results</p> <p>We engineered a C4-2B PCa sub-line called C4-2B/Rx2<sup>dox</sup>, in which Doxycycline (Dox) treatment stimulates Runx2 expression from very low to levels observed in other PCa cells. Transcriptome profiling using whole genome expression array followed by <it>in silico </it>analysis indicated that Runx2 upregulated a multitude of genes with prominent cancer associated functions. They included secreted factors (CSF2, SDF-1), proteolytic enzymes (MMP9, CST7), cytoskeleton modulators (SDC2, Twinfilin, SH3PXD2A), intracellular signaling molecules (DUSP1, SPHK1, RASD1) and transcription factors (Sox9, SNAI2, SMAD3) functioning in epithelium to mesenchyme transition (EMT), tissue invasion, as well as homing and attachment to bone. Consistent with the gene expression data, induction of Runx2 in C4-2B cells enhanced their invasiveness. It also promoted cellular quiescence by blocking the G1/S phase transition during cell cycle progression. Furthermore, the cell cycle block was reversed as Runx2 levels declined after Dox withdrawal.</p> <p>Conclusions</p> <p>The effects of Runx2 in C4-2B/Rx2<sup>dox </sup>cells, as well as similar observations made by employing LNCaP, 22RV1 and PC3 cells, highlight multiple mechanisms by which Runx2 promotes the metastatic phenotype of PCa cells, including tissue invasion, homing to bone and induction of high bone turnover. Runx2 is therefore an attractive target for the development of novel diagnostic, prognostic and therapeutic approaches to PCa management. Targeting Runx2 may prove more effective than focusing on its individual downstream genes and pathways.</p
Exploring Intermediate (5-40 au) Scales around AB Aurigae with the Palomar Fiber Nuller
We report on recent Ks-band interferometric observations of the young pre-main-sequence star AB Aurigae obtained with the Palomar Fiber Nuller (PFN). Reaching a contrast of a few 10^−4 inside a field of view extending from 35 to 275 mas (5–40 AU at AB Aur's distance), the PFN is able to explore angular scales that are intermediate between those accessed by coronagraphic imaging and long baseline interferometry. This intermediate region is of special interest given that many young stellar objects are believed to harbor extended halos at such angular scales. Using destructive interference (nulling) between two sub-apertures of the Palomar 200 inch telescope and rotating the telescope pupil, we measured a resolved circumstellar excess at all probed azimuth angles. The astrophysical null measured over the full rotation is fairly constant, with a mean value of 1.52%, and a slight additional azimuthal modulation of ±0.2%. The isotropic astrophysical null is indicative of circumstellar emission dominated by an azimuthally extended source, possibly a halo, or one or more rings of dust, accounting for several percent of the total Ks-band flux. The modest azimuthal variation may be explained by some skewness or anisotropy of the spatially extended source, e.g., an elliptical or spiral geometry, or clumping, but it could also be due to the presence of a point source located at a separation of ~120 mas (17 AU) with ~6 × 10^−3 of the stellar flux. We combine our results with previous Infrared Optical Telescope Array observations of AB Aur at H band, and demonstrate that a dust ring located at ~30 mas (4.3 AU) represents the best-fitting model to explain both sets of visibilities. We are also able to test a few previously hypothesized models of the incoherent component evident at longer interferometric baselines
Control interface concepts for CHARA 6-telescope fringe tracking with CHAMP+MIRC
This is the author accepted manuscript. The final version is available from SPIE via the DOI in this record.Cophasing six telescopes from the CHARA array, the CHARA-Michigan Phasetracker (CHAMP) and Michigan Infrared Combiner (MIRC) are pushing the frontiers of infrared long-baseline interferometric imaging in key scientific areas such as star- and planet-formation. Here we review our concepts and recent improvements on the CHAMP and MIRC control interfaces, which establish the communication to the real-time data recording & fringe tracking code, provide essential performance diagnostics, and assist the observer in the alignment and flux optimization procedure. For fringe detection and tracking with MIRC, we have developed a novel matrix approach, which provides predictions for the fringe positions based on cross-fringe information.This work was performed in part under contract with the California Institute of Technology
(Caltech) funded by NASA through the Sagan Fellowship Program
Simultaneous Water Vapor and Dry Air Optical Path Length Measurements and Compensation with the Large Binocular Telescope Interferometer
The Large Binocular Telescope Interferometer uses a near-infrared camera to
measure the optical path length variations between the two AO-corrected
apertures and provide high-angular resolution observations for all its science
channels (1.5-13 m). There is however a wavelength dependent component to
the atmospheric turbulence, which can introduce optical path length errors when
observing at a wavelength different from that of the fringe sensing camera.
Water vapor in particular is highly dispersive and its effect must be taken
into account for high-precision infrared interferometric observations as
described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this
paper, we describe the new sensing approach that has been developed at the LBT
to measure and monitor the optical path length fluctuations due to dry air and
water vapor separately. After reviewing the current performance of the system
for dry air seeing compensation, we present simultaneous H-, K-, and N-band
observations that illustrate the feasibility of our feedforward approach to
stabilize the path length fluctuations seen by the LBTI nuller.Comment: SPIE conference proceeding
New insights on the AU-scale circumstellar structure of FU Orionis
We report new near-infrared, long-baseline interferometric observations at
the AU scale of the pre-main-sequence star FU Orionis with the PTI, IOTA and
VLTI interferometers. This young stellar object has been observed on 42 nights
over a period of 6 years from 1998 to 2003. We have obtained 287 independent
measurements of the fringe visibility with 6 different baselines ranging from
20 to 110 meters in length, in the H and K bands. Our extensive (u,v)-plane
coverage, coupled with the published spectral energy distribution data, allows
us to test the accretion disk scenario. We find that the most probable
explanation for these observations is that FU Ori hosts an active accretion
disk whose temperature law is consistent with standard models. We are able to
constrain the geometry of the disk, including an inclination of 55 deg and a
position angle of 47 deg. In addition, a 10 percent peak-to-peak oscillation is
detected in the data (at the two-sigma level) from the longest baselines, which
we interpret as a possible disk hot-spot or companion. However, the oscillation
in our best data set is best explained with an unresolved spot located at a
projected distance of 10 AU at the 130 deg position angle and with a magnitude
difference of DeltaK = 3.9 and DeltaH = 3.6 mag moving away from the center at
a rate of 1.2 AU/yr. we propose to interpret this spot as the signature of a
companion of the central FU Ori system on an extremely eccentric orbit. We
speculate that the close encounter of this putative companion and the central
star could be the explanation of the initial photometric rise of the luminosity
of this object
First visual orbit for the prototypical colliding-wind binary WR 140
Wolf-Rayet stars represent one of the final stages of massive stellar
evolution. Relatively little is known about this short-lived phase and we
currently lack reliable mass, distance, and binarity determinations for a
representative sample. Here we report the first visual orbit for WR
140(=HD193793), a WC7+O5 binary system known for its periodic dust production
episodes triggered by intense colliding winds near periastron passage. The IOTA
and CHARA interferometers resolved the pair of stars in each year from
2003--2009, covering most of the highly-eccentric, 7.9 year orbit. Combining
our results with the recent improved double-line spectroscopic orbit of Fahed
et al. (2011), we find the WR 140 system is located at a distance of 1.67 +/-
0.03 kpc, composed of a WR star with M_WR = 14.9 +/- 0.5 Msun and an O star
with M_O = 35.9 +/- 1.3 Msun. Our precision orbit yields key parameters with
uncertainties times 6 smaller than previous work and paves the way for detailed
modeling of the system. Our newly measured flux ratios at the near-infrared H
and Ks bands allow an SED decomposition and analysis of the component
evolutionary states.Comment: Complete OIFITS dataset included via Data Conservancy Projec
JouFLU: upgrades to the Fiber Linked Unit for Optical Recombination (FLUOR) interferometric beam combiner
The Fiber Linked Unit for Optical Recombination (FLUOR) is a precision interferometric beam combiner operating at the CHARA Array on Mt. Wilson, CA. It has recently been upgraded as part of a mission known as “Jouvence of FLUOR” or JouFLU. As part of this program JouFLU has new mechanic stages and optical payloads, new alignment systems, and new command/control software. Furthermore, new capabilities have been implemented such as a Fourier Transform Spectrograph (FTS) mode and spectral dispersion mode. These upgrades provide new capabilities to JouFLU as well as improving statistical precision and increasing observing efficiency. With these new systems, measurements of interferometric visibility to the level of 0.1% precision are expected on targets as faint as 6th magnitude in the K band. Here we detail the upgrades of JouFLU and report on its current status
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