114 research outputs found
Simultaneous monitoring of the photometric and polarimetric activity of the young star PV Cep in the optical/near-infrared bands
We present the results of a simultaneous monitoring, lasting more than 2
years, of the optical and near-infrared photometric and polarimetric activity
of the variable protostar PV Cep. During the monitoring period, an outburst has
occurred in all the photometric bands, whose declining phase (J
3 mag) lasted about 120 days. A time lag of 30 days between
optical and infrared light curves has been measured and interpreted in the
framework of an accretion event. This latter is directly recognizable in the
significant variations of the near-infrared colors, that appear bluer in the
outburst phase, when the star dominates the emission, and redder in declining
phase, when the disk emission prevails. All the observational data have been
combined to derive a coherent picture of the complex morphology of the whole PV
Cep system, that, in addition to the star and the accretion disk, is composed
also by a variable biconical nebula. In particular, the mutual interaction
between all these components is the cause of the high value of the polarization
( 20%) and of its fluctuations. The observational data concur to
indicate that PV Cep is not a genuine EXor star, but rather a more complex
object; moreover the case of PV Cep leads to argue about the classification of
other recently discovered young sources in outburst, that have been considered,
maybe over-simplifying, as EXor.Comment: Accepted for publication on Ap
The Brightening of Re50N: Accretion Event or Dust Clearing?
The luminous Class I protostar HBC 494, embedded in the Orion A cloud, is
associated with a pair of reflection nebulae, Re50 and Re50N, which appeared
sometime between 1955 and 1979. We have found that a dramatic brightening of
Re50N has taken place sometime between 2006 and 2014. This could result if the
embedded source is undergoing a FUor eruption. However, the near-infrared
spectrum shows a featureless very red continuum, in contrast to the strong CO
bandhead absorption displayed by FUors. Such heavy veiling, and the high
luminosity of the protostar, is indicative of strong accretion but seemingly
not in the manner of typical FUors. We favor the alternative explanation that
the major brightening of Re50N and the simultaneous fading of Re50 is caused by
curtains of obscuring material that cast patterns of illumination and shadows
across the surface of the molecular cloud. This is likely occurring as an
outflow cavity surrounding the embedded protostar breaks through to the surface
of the molecular cloud. Several Herbig-Haro objects are found in the region.Comment: 8 pages, accepted by Ap
Second generation Robo-AO instruments and systems
The prototype Robo-AO system at the Palomar Observatory 1.5-m telescope is
the world's first fully automated laser adaptive optics instrument. Scientific
operations commenced in June 2012 and more than 12,000 observations have since
been performed at the ~0.12" visible-light diffraction limit. Two new infrared
cameras providing high-speed tip-tilt sensing and a 2' field-of-view will be
integrated in 2014. In addition to a Robo-AO clone for the 2-m IGO and the
natural guide star variant KAPAO at the 1-m Table Mountain telescope, a second
generation of facility-class Robo-AO systems are in development for the 2.2-m
University of Hawai'i and 3-m IRTF telescopes which will provide higher Strehl
ratios, sharper imaging, ~0.07", and correction to {\lambda} = 400 nm.Comment: 11 pages, 4 figures, 3 table
Molecular hydrogen jets and outflows in the Serpens south filamentary cloud
We aimed to map the jets and outflows from the Serpens South star forming
region and find an empirical relationship between the magnetic field and
outflow orientation. Near-infrared H2 v=1-0 S(1) 2.122{\mu}m -line imaging of
the \sim 30'-long filamentary shaped Serpens South star forming region was
carried out. K s broadband imaging of the same region was used for continuum
subraction. Candidate driving sources of the mapped jets/outflows are
identified from the list of known protostars and young stars in this region,
which was derived from studies using recent Spitzer and Herschel telescope
observations. 14 Molecular Hydrogen emission-line objects(MHOs) are identified
using our continuum-subtracted images. They are found to constitute ten
individual flows. Out of these, nine flows are located in the
lower-half(southern) part of the Serpens South filament, and one flow is
located at the northern tip of the filament. Four flows are driven by
well-identified Class 0 protostars, while the remaining six flows are driven by
candidate protostars mostly in the Class I stage, based on the Spitzer and
Herschel observations. The orientation of the outflows is systematically
perpendicular to the direction of the near-infrared polarization vector,
recently published in the literature. No significant correlation was observed
between the orientation of the flows and the axis of the filamentary cloud.Comment: Accepted by A&A for publication. 7 pages, 5 figure
Visual Binaries in the Orion Nebula Cluster
We have carried out a major survey for visual binaries towards the Orion
Nebula Cluster using HST images obtained with an H-alpha filter. Among 781
likely ONC members more than 60" from theta-1 Ori C, we find 78 multiple
systems (75 binaries and 3 triples), of which 55 are new discoveries, in the
range from 0.1" to 1.5". About 9 binaries are likely line-of-sight
associations. We find a binary fraction of 8.8%+-1.1% within the limited
separation range from 67.5 to 675 AU. The field binary fraction in the same
range is a factor 1.5 higher. Within the range 150 AU to 675 AU we find that T
Tauri associations have a factor 2.2 more binaries than the ONC. The binary
separation distribution function of the ONC shows unusual structure, with a
sudden steep decrease in the number of binaries as the separation increases
beyond 0.5", corresponding to 225 AU. We have measured the ratio of binaries
wider than 0.5" to binaries closer than 0.5" as a function of distance from the
Trapezium, and find that this ratio is significantly depressed in the inner
region of the ONC. The deficit of wide binaries in the central part of the
cluster is likely due to dissolution or orbital change during their passage
through the potential well of the inner cluster region. Many of the companions
are likely to be brown dwarfs.Comment: 27 pages, 10 figures, 2 tables, accepted by the Astronomical Journa
First results on a new PIAA coronagraph testbed at NASA Ames
Direct imaging of extrasolar planets, and Earth-like planets in particular, is an exciting but difficult problem requiring a telescope imaging system with 1010 contrast at separations of 100 mas and less. Furthermore, the current NASA science budget may only allow for a small 1-2 m space telescope for this task, which puts strong demands on the performance of the imaging instrument. Fortunately, an efficient coronagraph called the Phase Induced Amplitude Apodization (PIAA) coronagraph has been maturing and may enable Earth-like planet imaging for such small telescopes. In this paper, we report on the latest results from a new testbed at NASA Ames focused on testing the PIAA coronagraph. This laboratory facility was built in 2008 and is designed to be flexible, operated in a highly stabilized air environment, and to complement existing efforts at NASA JPL. For our wavefront control we are focusing on using small Micro-Electro- Mechanical-System deformable mirrors (MEMS DMs), which promises to reduce the size of the beam and overall instrument, a consideration that becomes very important for small telescopes. At time of this writing, we are operating a refractive PIAA system and have achieved contrasts of about 1.2×10-7 in a dark zone from 2.0 to 4.8 λ/D (with 6.6×10-8 in selected regions). In this paper, we present these results, describe our methods, present an analysis of current limiting factors, and solutions to overcome them
Alcelaphine herpesvirus 1 genes A7 and A8 regulate viral spread and are essential for malignant catarrhal fever
Alcelaphine herpesvirus 1 (AlHV-1) is a gammaherpesvirus that is carried asymptomatically by wildebeest. Upon cross-species transmission to other ruminants, including domestic cattle, AlHV-1 induces malignant catarrhal fever (MCF), which is a fatal lymphoproliferative disease resulting from proliferation and uncontrolled activation of latently infected CD8+ T cells. Two laboratory strains of AlHV-1 are used commonly in research: C500, which is pathogenic, and WC11, which has been attenuated by long-term maintenance in cell culture. The published genome sequence of a WC11 seed stock from a German laboratory revealed the deletion of two major regions. The sequence of a WC11 seed stock used in our laboratory also bears these deletions and, in addition, the duplication of an internal sequence in the terminal region. The larger of the two deletions has resulted in the absence of gene A7 and a large portion of gene A8. These genes are positional orthologs of the Epstein-Barr virus genes encoding envelope glycoproteins gp42 and gp350, respectively, which are involved in viral propagation and switching of cell tropism. To investigate the degree to which the absence of A7 and A8 participates in WC11 attenuation, recombinant viruses lacking these individual functions were generated in C500. Using bovine nasal turbinate and embryonic lung cell lines, increased cell-free viral propagation and impaired syncytia formation were observed in the absence of A7, whereas cell-free viral spread was inhibited in the absence of A8. Therefore, A7 appears to be involved in cell-to-cell viral spread, and A8 in viral cell-free propagation. Finally, infection of rabbits with either mutant did not induce the signs of MCF or the expansion of infected CD8+ T cells. These results demonstrate that A7 and A8 are both essential for regulating viral spread and suggest that AlHV-1 requires both genes to efficiently spread in vivo and reach CD8+ T lymphocytes and induce MCF
Highly Variable Extinction and Accretion in the Jet-driving Class I Type Young Star PTF 10nvg (V2492 Cyg, IRAS 20496+4354)
We report extensive new photometry and spectroscopy of the highly variable
young stellar object PTF 10nvg including optical and near-infrared time series
data as well as mid-infrared and millimeter data. Following the previously
reported 2010 rise, during 2011 and 2012 the source underwent additional
episodes of brightening and dimming events including prolonged faint states.
The observed high-amplitude variations are largely consistent with extinction
changes having a 220 day quasi-periodic signal. Spectral evolution includes not
only changes in the spectral slope but correlated variation in the prominence
of TiO/VO/CO bands and atomic line emission, as well as anticorrelated
variation in forbidden line emission which, along with H_2, dominates optical
and infrared spectra at faint epochs. Neutral and singly-ionized atomic species
are likely formed in an accretion flow and/or impact while the origin of
zero-velocity atomic LiI 6707 in emission is unknown. Forbidden lines,
including several rare species, exhibit blueshifted emission profiles and
likely arise from an outflow/jet. Several of these lines are also seen
spatially offset from the continuum source position, presumably in a shocked
region of an extended jet. CARMA maps resolve on larger scales a spatially
extended outflow in mm-wavelength CO. We attribute the observed photometric and
spectroscopic behavior in terms of occultation of the central star as well as
the bright inner disk and the accretion/outflow zones that renders shocked gas
in the inner part of the jet amenable to observation at the faint epochs. We
discuss PTF 10nvg as a source exhibiting both accretion-driven (perhaps
analogous to V1647 Ori) and extinction-driven (perhaps analogous to UX Ori or
GM Cep) high-amplitude variability phenomena.Comment: accepted to AJ - in press (74 pages
CLOUDS search for variability in brown dwarf atmospheres
Context: L-type ultra-cool dwarfs and brown dwarfs have cloudy atmospheres
that could host weather-like phenomena. The detection of photometric or
spectral variability would provide insight into unresolved atmospheric
heterogeneities, such as holes in a global cloud deck.
Aims: It has been proposed that growth of heterogeneities in the global cloud
deck may account for the L- to T-type transition as brown dwarf photospheres
evolve from cloudy to clear conditions. Such a mechanism is compatible with
variability. We searched for variability in the spectra of five L6 to T6 brown
dwarfs in order to test this hypothesis.
Methods: We obtained spectroscopic time series using VLT/ISAAC, over
0.99-1.13um, and IRTF/SpeX for two of our targets, in J, H and K bands. We
search for statistically variable lines and correlation between those.
Results: High spectral-frequency variations are seen in some objects, but
these detections are marginal and need to be confirmed. We find no evidence for
large amplitude variations in spectral morphology and we place firm upper
limits of 2 to 3% on broad-band variability, on the time scale of a few hours.
The T2 transition brown dwarf SDSS J1254-0122 shows numerous variable features,
but a secure variability diagnosis would require further observations.
Conclusions: Assuming that any variability arises from the rotation of
patterns of large-scale clear and cloudy regions across the surface, we find
that the typical physical scale of cloud cover disruption should be smaller
than 5-8% of the disk area for four of our targets. The possible variations
seen in SDSS J1254-0122 are not strong enough to allow us to confirm the cloud
breaking hypothesis.Comment: 17 pages, 14 figures, accepted by A&
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