220 research outputs found
Spatially extended emission around the Cepheid RS Puppis in near-infrared hydrogen lines. Adaptive optics imaging with VLT/NACO
It has been recently discovered that Cepheids harbor circumstellar envelopes
(CSEs). RS Pup is the Cepheid that presents the most prominent circumstellar
envelope known, the origin of which is not yet understood. Our purpose is to
estimate the flux contribution of the CSE around RS Pup at the one arcsecond
scale (~2000 AU) and to investigate its geometry, especially regarding
asymmetries, to constrain its physical properties. We obtained near-infrared
images in two narrow band filters centered on \lambda = 1.644 and 2.180 \mu m
(NB 1.64 and IB 2.18, respectively) that comprise two recombination lines of
hydrogen: the 12-4 and 7-4 (Brackett \gamma) transitions, respectively. We used
NACO's cube mode observations in order to improve the angular resolution with
the shift-and-add technique, and to qualitatively study the symmetry of the
spatially extended emission from the CSE with a statistical study of the
speckle noise. We probably detect at a 2\sigma level an extended emission with
a relative flux (compared with the star in the same filter) of 38 17% in
the NB 1.64 filter and 24 11% in the IB 2.18 filter. This emission is
centered on RS Pup and does not present any detectable asymmetry. We attribute
the detected emission to the likely presence of an hydrogen envelope
surrounding the star
Image quality and high contrast improvements on VLT/NACO
NACO is the famous and versatile diffraction limited NIR imager and
spectrograph with which ESO celebrated 10 years of Adaptive Optics at the VLT.
Since two years a substantial effort has been put in to understanding and
fixing issues that directly affect the image quality and the high contrast
performances of the instrument. Experiments to compensate the non-common-path
aberrations and recover the highest possible Strehl ratios have been carried
out successfully and a plan is hereafter described to perform such measurements
regularly. The drift associated to pupil tracking since 2007 was fixed in
October 2011. NACO is therefore even better suited for high contrast imaging
and can be used with coronagraphic masks in the image plane. Some contrast
measurements are shown and discussed. The work accomplished on NACO will serve
as reference for the next generation instruments on the VLT, especially those
working at the diffraction limit and making use of angular differential imaging
(i.e. SPHERE, VISIR, possibly ERIS).Comment: 14 pages, 5 figures, SPIE 2012 Astronomical Instrumentation
Proceedin
An apodizing phase plate coronagraph for VLT/NACO
We describe a coronagraphic optic for use with CONICA at the VLT that
provides suppression of diffraction from 1.8 to 7 lambda/D at 4.05 microns, an
optimal wavelength for direct imaging of cool extrasolar planets. The optic is
designed to provide 10 magnitudes of contrast at 0.2 arcseconds, over a
D-shaped region in the image plane, without the need for any focal plane
occulting mask.Comment: 9 pages, 5 figures, to appear in Proc. SPIE Vol. 773
Status and new operation modes of the versatile VLT/NACO
This paper aims at giving an update on the most versatile adaptive optics fed
instrument to date, the well known and successful NACO . Although NACO is only
scheduled for about two more years at the Very Large Telescope (VLT), it keeps
on evolving with additional operation modes bringing original astronomical
results. The high contrast imaging community uses it creatively as a test-bench
for SPHERE and other second generation planet imagers. A new visible wavefront
sensor (WFS) optimized for Laser Guide Star (LGS) operations has been installed
and tested, the cube mode is more and more requested for frame selection on
bright sources, a seeing enhancer mode (no tip/tilt correction) is now offered
to provide full sky coverage and welcome all kind of extragalactic
applications, etc. The Instrument Operations Team (IOT) and Paranal engineers
are currently working hard at maintaining the instrument overall performances
but also at improving them and offering new capabilities, providing the
community with a well tuned and original instrument for the remaining time it
is being used. The present contribution delivers a non-exhaustive overview of
the new modes and experiments that have been carried out in the past months.Comment: 10 pages, 7 figures, SPIE 2010 Astronomical Instrumentation
Proceedin
Trends in Silicates in the Pictoris Disk
While beta Pic is known to host silicates in ring-like structures, whether
the properties of these silicate dust vary with stellocentric distance remains
an open question. We re-analyze the beta Pictoris debris disk spectrum from the
Spitzer Infrared Spectrograph (IRS) and a new IRTF/SpeX spectrum to investigate
trends in Fe/Mg ratio, shape, and crystallinity in grains as a function of
wavelength, a proxy for stellocentric distance. By analyzing a re-calibrated
and re-extracted spectrum, we identify a new 18 micron forsterite emission
feature and recover a 23 micron forsterite emission feature with a
substantially larger line-to-continuum ratio than previously reported. We find
that these prominent spectral features are primarily produced by small
submicron-sized grains, which are continuously generated and replenished from
planetesimal collisions in the disk and can elucidate their parent bodies'
composition. We discover three trends about these small grains: as
stellocentric distance increases, (1) small silicate grains become more
crystalline (less amorphous), (2) they become more irregular in shape, and (3)
for crystalline silicate grains, the Fe/Mg ratio decreases. Applying these
trends to beta Pic's planetary architecture, we find that the dust population
exterior to the orbits of beta Pic b and c differs substantially in
crystallinity and shape. We also find a tentative 3-5 micron dust excess due to
spatially unresolved hot dust emission close to the star. From our findings, we
infer that the surfaces of large planetesimals are more Fe-rich and
collisionally-processed closer to the star but more Fe-poor and primordial
farther from the star.Comment: 19 pages, 12 figures, Accepted for Publication in Ap
Early formation and recent starburst activity in the nuclear disk of the Milky Way
The nuclear disk is a dense stellar structure at the centre of the Milky Way, with a radius of ~150 pc (ref. 1). It has been a place of intense star formation in the past several tens of millions of years1-3, but its overall formation history has remained unknown2. Here, we report that the bulk of its stars formed at least 8 Gyr ago. After a long period of quiescence, a starburst event followed about 1 Gyr ago that formed roughly 5% of its mass within ~100 Myr, in what may arguably have been one of the most energetic events in the history of the Milky Way. Star formation continued subsequently on a lower level, creating a few per cent of the stellar mass in the past ~500 Myr, with an increased rate up to ~30 Myr ago. Our findings contradict the previously accepted paradigm of quasi-continuous star formation at the Galactic Centre4. The long quiescent phase agrees with the overall quiescent history of the Milky Way2,5 and suggests that our Galaxy's bar may not have existed until recently, or that gas transport through the bar was extremely inefficient during a long stretch of the Milky Way's life. Consequently, the central black hole may have acquired most of its mass already in the early days of the Milky Way
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Characterization of the Benchmark Binary Nltt 33370
We report the confirmation of the binary nature of the nearby, very low-mass system NLTT 33370 with adaptive optics imaging and present resolved near-infrared photometry and integrated light optical and near-infrared spectroscopy to characterize the system. VLT-NaCo and LBTI-LMIRCam images show significant orbital motion between 2013 February and 2013 April. Optical spectra reveal weak, gravity sensitive alkali lines and strong lithium 6708 ˚A absorption that indicate the system is younger than field age. VLT-SINFONI near-IR spectra also show weak, gravity sensitive features and spectral morphology that is consistent with other young, very low-mass dwarfs. We combine the constraints from all age diagnostics to estimate a system age of ∼30-200 Myr. The 1.2-4.7 µm spectral energy distribution of the components point toward Teff = 3200 ± 500 K and Teff = 3100 ± 500 K for NLTT 33370 A and B, respectively. The observed spectra, derived temperatures, and estimated age combine to constrain the component spectral types to the range M6-M8. Evolutionary models predict masses of 113 ±8 MJup and 106±7 MJup from the estimated luminosities of the components. KPNO-Phoenix spectra allow us to estimate the systemic radial velocity of the binary. The Galactic kinematics of NLTT 33370AB are broadly consistent with other young stars in the Solar neighborhood. However, definitive membership in a young, kinematic group cannot be assigned at this time and further follow-up observations are necessary to fully constrain the system’s kinematics. The proximity,
age, and late-spectral type of this binary make it very novel and an ideal target for rapid, complete orbit determination. The system is one of only a few model calibration benchmarks at young ages and very low-masses.Astronom
Search for non-Gaussian events in the data of the VIRGO E4 engineering run
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