11 research outputs found
Swimming with ShARCS: Comparison of On-sky Sensitivity With Model Predictions for ShaneAO on the Lick Observatory 3-meter Telescope
The Lick Observatory's Shane 3-meter telescope has been upgraded with a new
infrared instrument (ShARCS - Shane Adaptive optics infraRed Camera and
Spectrograph) and dual-deformable mirror adaptive optics (AO) system (ShaneAO).
We present first-light measurements of imaging sensitivity in the Ks band. We
compare measured results to predicted signal-to-noise ratio and magnitude
limits from modeling the emissivity and throughput of ShaneAO and ShARCS. The
model was validated by comparing its results to the Keck telescope adaptive
optics system model and then by estimating the sky background and limiting
magnitudes for IRCAL, the previous infra-red detector on the Shane telescope,
and comparing to measured, published results. We predict that the ShaneAO
system will measure lower sky backgrounds and achieve 20\% higher throughput
across the bands despite having more optical surfaces than the current
system. It will enable imaging of fainter objects (by 1-2 magnitudes) and will
be faster to reach a fiducial signal-to-noise ratio by a factor of 10-13. We
highlight the improvements in performance over the previous AO system and its
camera, IRCAL.Comment: 13 pages, 5 figures, SPIE Astronomical Telescopes + Instrumentation,
Montreal 201
ShaneAO: wide science spectrum adaptive optics system for the Lick Observatory
A new high-order adaptive optics system is now being commissioned at the Lick
Observatory Shane 3-meter telescope in California. This system uses a high
return efficiency sodium beacon and a combination of low and high-order
deformable mirrors to achieve diffraction-limited imaging over a wide spectrum
of infrared science wavelengths covering 0.8 to 2.2 microns. We present the
design performance goals and the first on-sky test results. We discuss several
innovations that make this system a pathfinder for next generation AO systems.
These include a unique woofer-tweeter control that provides full dynamic range
correction from tip/tilt to 16 cycles, variable pupil sampling wavefront
sensor, new enhanced silver coatings developed at UC Observatories that improve
science and LGS throughput, and tight mechanical rigidity that enables a
multi-hour diffraction- limited exposure in LGS mode for faint object
spectroscopy science.Comment: 11 pages, 10 figures. Presented at SPIE Astronomical Telescopes +
Instrumentation conference, paper 9148-7
Principal Component Analysis of SDSS Stellar Spectra
We apply Principal Component Analysis (PCA) to ~100,000 stellar spectra
obtained by the Sloan Digital Sky Survey (SDSS). In order to avoid strong
non-linear variation of spectra with effective temperature, the sample is
binned into 0.02 mag wide intervals of the g-r color (-0.20<g-r<0.90, roughly
corresponding to MK spectral types A3 to K3), and PCA is applied independently
for each bin. In each color bin, the first four eigenspectra are sufficient to
describe the observed spectra within the measurement noise. We discuss
correlations of eigencoefficients with metallicity and gravity estimated by the
Sloan Extension for Galactic Understanding and Exploration (SEGUE) Stellar
Parameters Pipeline. The resulting high signal-to-noise mean spectra and the
other three eigenspectra are made publicly available. These data can be used to
generate high quality spectra for an arbitrary combination of effective
temperature, metallicity, and gravity within the parameter space probed by the
SDSS. The SDSS stellar spectroscopic database and the PCA results presented
here offer a convenient method to classify new spectra, to search for unusual
spectra, to train various spectral classification methods, and to synthesize
accurate colors in arbitrary optical bandpasses.Comment: 25 pages, 15 figures, accepted by the Astronomical Journa
Commissioning ShARCS: the Shane Adaptive optics infraRed Camera-Spectrograph for the Lick Observatory 3-m telescope
We describe the design and first-light early science performance of the Shane
Adaptive optics infraRed Camera-Spectrograph (ShARCS) on Lick Observatory's 3-m
Shane telescope. Designed to work with the new ShaneAO adaptive optics system,
ShARCS is capable of high-efficiency, diffraction-limited imaging and
low-dispersion grism spectroscopy in J, H, and K-bands. ShARCS uses a
HAWAII-2RG infrared detector, giving high quantum efficiency (>80%) and Nyquist
sampling the diffraction limit in all three wavelength bands. The ShARCS
instrument is also equipped for linear polarimetry and is sensitive down to 650
nm to support future visible-light adaptive optics capability. We report on the
early science data taken during commissioning.Comment: 9 pages, 7 figures. Presented at SPIE Astronomical Telescopes +
Instrumentation conference, paper 9148-11
The Milky Way Tomography With SDSS. III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r 20 degrees). We find that in the region defined by 1 kpc < Z < 5 kpc and 3 kpc < R < 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (< 100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.NSF AST-615991, AST-0707901, AST-0551161, AST-02-38683, AST-06-07634, AST-0807444, PHY05-51164NASA NAG5-13057, NAG5-13147, NNXO-8AH83GPhysics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) PHY 08-22648U.S. National Science FoundationMarie Curie Research Training Network ELSA (European Leadership in Space Astrometry) MRTN-CT-2006-033481Fermi Research Alliance, LLC, United States Department of Energy DE-AC02-07CH11359Alfred P. Sloan FoundationParticipating InstitutionsJapanese MonbukagakushoMax Planck SocietyHigher Education Funding Council for EnglandMcDonald Observator
LINC-NIRVANA Commissioning at the Large Binocular Telescope - Lessons Learned
LINC-NIRVANA (LN) is one of the instruments on-board the Large Binocular Telescope (LBT). LN is a high- resolution, near-infrared imager equipped with an advanced adaptive optics module. LN implements layer- oriented Multi-Conjugate Adaptive Optics (MCAO) approach using two independent wavefront sensors per side of the binocular telescope measuring the turbulence volume above the telescope. The capability of acquiring up to 20 Natural Guide Stars simultaneously from two distinct fields of view, and using them for wavefront sensing with 20 separate pyramids per side of the telescope makes the LN MCAO system one of a kind.
Commissioning of the left MCAO channel is almost complete, while that of the right arm is on-going. The Science Verification on the left side is expected to start soon after the MCAO performance is optimised for faint guide stars. In this article, we put together the lessons learned during the commissioning of the LN MCAO module. We hope and believe that this article will help the future MCAO instrument commissioning teams
The Milky Way Tomography with SDSS: III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence
stars with r<20 and proper-motion measurements derived from SDSS and POSS
astrometry, including ~170,000 stars with radial-velocity measurements from the
SDSS spectroscopic survey. Distances to stars are determined using a
photometric parallax relation, covering a distance range from ~100 pc to 10 kpc
over a quarter of the sky at high Galactic latitudes (|b|>20 degrees). We find
that in the region defined by 1 kpc <Z< 5 kpc and 3 kpc <R< 13 kpc, the
rotational velocity for disk stars smoothly decreases, and all three components
of the velocity dispersion increase, with distance from the Galactic plane. In
contrast, the velocity ellipsoid for halo stars is aligned with a spherical
coordinate system and appears to be spatially invariant within the probed
volume. The velocity distribution of nearby ( kpc) K/M stars is complex,
and cannot be described by a standard Schwarzschild ellipsoid. For stars in a
distance-limited subsample of stars (<100 pc), we detect a multimodal velocity
distribution consistent with that seen by HIPPARCOS. This strong
non-Gaussianity significantly affects the measurements of the velocity
ellipsoid tilt and vertex deviation when using the Schwarzschild approximation.
We develop and test a simple descriptive model for the overall kinematic
behavior that captures these features over most of the probed volume, and can
be used to search for substructure in kinematic and metallicity space. We use
this model to predict further improvements in kinematic mapping of the Galaxy
expected from Gaia and LSST.Comment: 90 pages, 26 figures, submitted to Ap
Commissioning ShARCS: the Shane Adaptive optics infraRed Camera-Spectrograph for the Lick Observatory 3-m telescope
We describe the design and first-light early science performance of the Shane Adaptive optics infraRed Camera- Spectrograph (ShARCS) on Lick Observatoryās 3-m Shane telescope. Designed to work with the new ShaneAO adaptive optics system, ShARCS is capable of high-efficiency, diffraction-limited imaging and low-dispersion grism spectroscopy in J, H, and K-bands. ShARCS uses a HAWAII-2RG infrared detector, giving high quantum efficiency (>80%) and Nyquist sampling the diffraction limit in all three wavelength bands. The ShARCS instrument is also equipped for linear polarimetry and is sensitive down to 650 nm to support future visible-light adaptive optics capability. We report on the early science data taken during commissioning
Searching for Dual AGNs in Galaxy Mergers: Understanding Double-Peaked [O III] as a Selection Method
When galaxies merge, gas may accrete onto both central supermassive black holes. Thus, one expects to see close pairs of active galactic nuclei (AGNs), or dual AGNs, in a fraction of galaxy mergers. The existence and statistics of dual AGNs provide an important probe into hierarchical galaxy formation models, accretion-triggering mechanisms, galaxy merger rates, and black hole growth. However, finding them remains a challenge. The presence of double-peaked [O III] has been proposed as a technique to select dual AGNs efficiently. We studied a sample of double-peaked narrow [O III] emitting AGNs from the Sloan Digital Sky Survey. By obtaining new and archival high spatial resolution images taken with the Keck II Laser Guide Star Adaptive Optics system and the near-infrared (IR) camera NIRC2, we showed that 31%+/-3% of double-peaked [O III] emission line SDSS AGNs have two spatial components within a 3" radius. However, the imaging discussed above does not show whether or how the double emission line structure relates to the presence of a companion. Spatially resolved spectroscopy or X-ray observations can confirm these galaxy pairs as systems containing two AGNs. We followed up these spatially-double candidate dual AGNs with integral field spectroscopy from Keck OSIRIS and Gemini GMOS and with long-slit spectroscopy from Keck NIRSPEC and Shane Kast Double Spectrograph. We find double-peaked lines are sometimes dual AGN and sometimes outflows or narrow line kinematics. We also performed Chandra X-ray ACIS-S observations on 12 double-peaked candidate dual AGNs. Using our observations and 8 archival observations, we compare the distribution of X-ray photons to our spatially double near-IR images, measure X-ray luminosities and hardness ratios, and estimate column densities. By assessing what fraction of double-peaked emission line SDSS AGNs are true dual AGNs, we can better determine whether double-peaked [O III] is an efficient dual AGN indicator and constrain the statistics of dual AGNs
Cataclysmic variables from SDSS. VII. The seventh year (2006)
Coordinates, magnitudes, and spectra are presented for 39 cataclysmic variables (CVs) found in Sloan Digital Sky Survey (SDSS) spectra that were primarily obtained in 2006. Of these, 13 were CVs identified prior to the SDSS spectra (AK Cnc, GY Cnc, GO Com, ST LMi, NY Ser, MR Ser, QW Ser, EU UMa, IY UMa, HS1340+ 1524, RXJ1610.1+0352, Boo 1, Leo 5). Follow-up spectroscopic observations of seven systems (including one from year 2005 and another from year 2004) were obtained, resulting in estimates of the orbital periods for three objects. The new CVs include two candidates for high inclination, eclipsing systems, four new polars, and three systems whose spectra clearly reveal atmospheric absorption lines from the underlying white dwarf