17 research outputs found
Andromeda's Parachute: A Bright Quadruply Lensed Quasar at z=2.377
We present Keck Cosmic Web Imager spectroscopy of the four putative images of
the lensed quasar candidate J014709+463037 recently discovered by Berghea et
al. (2017). The data verify the source as a quadruply lensed, broad
absorption-line quasar having z_S = 2.377 +/- 0.007. We detect intervening
absorption in the FeII 2586, 2600, MgII 2796, 2803, and/or CIV 1548, 1550
transitions in eight foreground systems, three of which have redshifts
consistent with the photometric-redshift estimate reported for the lensing
galaxy (z_L ~ 0.57). By virtue of their positions on the sky, the source images
probe these absorbers over transverse physical scales of ~0.3-21 kpc,
permitting assessment of the variation in metal-line equivalent width W_r as a
function of sight-line separation. We measure differences in W_r,2796 of <40%
across all sight-line pairs subtending 7-21 kpc, suggestive of a high degree of
spatial coherence for MgII-absorbing material. W_r,2600 is observed to vary by
>50% over the same scales across the majority of sight-line pairs, while CIV
absorption exhibits a wide range in W_r,1548 differences of ~5-80% within
transverse distances less than ~3 kpc. J014709+463037 is one of only a handful
of z > 2 quadruply lensed systems for which all four source images are very
bright (r = 15.4-17.7 mag) and are easily separated in ground-based seeing
conditions. As such, it is an ideal candidate for higher-resolution
spectroscopy probing the spatial variation in the kinematic structure and
physical state of intervening absorbers.Comment: Submitted to ApJL. 9 pages, 3 figures. Uses aastex61 forma
Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph
From observations collected with the ESPaDOnS spectropolarimeter, we report
the discovery of magnetic fields at the surface of the mildly accreting
classical T Tauri star V2129 Oph. Zeeman signatures are detected, both in
photospheric lines and in the emission lines formed at the base of the
accretion funnels linking the disc to the protostar, and monitored over the
whole rotation cycle of V2129 Oph. We observe that rotational modulation
dominates the temporal variations of both unpolarized and circularly polarized
line profiles. We reconstruct the large-scale magnetic topology at the surface
of V2129 Oph from both sets of Zeeman signatures simultaneously. We find it to
be rather complex, with a dominant octupolar component and a weak dipole of
strengths 1.2 and 0.35 kG, respectively, both slightly tilted with respect to
the rotation axis. The large-scale field is anchored in a pair of 2-kG unipolar
radial field spots located at high latitudes and coinciding with cool dark
polar spots at photospheric level. This large-scale field geometry is unusually
complex compared to those of non-accreting cool active subgiants with moderate
rotation rates. As an illustration, we provide a first attempt at modelling the
magnetospheric topology and accretion funnels of V2129 Oph using field
extrapolation. We find that the magnetosphere of V2129 Oph must extend to about
7R* to ensure that the footpoints of accretion funnels coincide with the
high-latitude accretion spots on the stellar surface. It suggests that the
stellar magnetic field succeeds in coupling to the accretion disc as far out as
the corotation radius, and could possibly explain the slow rotation of V2129
Oph. The magnetospheric geometry we derive produces X-ray coronal fluxes
typical of those observed in cTTSs.Comment: MNRAS, in press (18 pages, 17 figures
An overview of the NIRSPEC upgrade for the Keck II telescope
NIRSPEC is a 1-5 micron echelle spectrograph in use on the Keck II Telescope
since 1999. The spectrograph is capable of both moderate (R~2,000) and high
(R~25,000) resolution observations and has been a workhorse instrument across
many astronomical fields, from planetary science to extragalactic observations.
In the latter half of 2018, we will upgrade NIRSPEC to improve the sensitivity
and stability of the instrument and increase its lifetime. The major components
of the upgrade include replacing the spectrometer and slit-viewing camera
detectors with Teledyne H2RG arrays and replacing all transputer-based
electronics. We present detailed design, testing, and analysis of the upgraded
instrument, including the finalized optomechanical design of the new 1-5 micron
slit-viewing camera, final alignment and assembly of the science array,
electronics systems, and updated software design.Comment: Proceedings of the 2018 SPIE Astronomical Telescopes &
Instrumentatio
The AIROPA software package - Milestones for testing general relativity in the strong gravity regime with AO
General relativity can be tested in the strong gravity regime by monitoring stars orbiting the supermassive black hole at the Galactic Center with adaptive optics. However, the limiting source of uncertainty is the spatial PSF variability due to atmospheric anisoplanatism and instrumental aberrations. The Galactic Center Group at UCLA has completed a project developing algorithms to predict PSF variability for Keck AO images. We have created a new software package (AIROPA), based on modified versions of StarFinder and Arroyo, that takes atmospheric turbulence profiles, instrumental aberration maps, and images as inputs and delivers improved photometry and astrometry on crowded fields. This software package will be made publicly available soon
The TEXES Survey For H2 Emission From Protoplanetary Disks
We report the results of a search for pure rotational molecular hydrogen
emission from the circumstellar environments of young stellar objects with
disks using the Texas Echelon Cross Echelle Spectrograph (TEXES) on the NASA
Infrared Telescope Facility and the Gemini North Observatory. We searched for
mid-infrared H2 emission in the S(1), S(2), and S(4) transitions. Keck/NIRSPEC
observations of the H2 S(9) transition were included for some sources as an
additional constraint on the gas temperature. We detected H2 emission from 6 of
29 sources observed: AB Aur, DoAr 21, Elias 29, GSS 30 IRS 1, GV Tau N, and HL
Tau. Four of the six targets with detected emission are class I sources that
show evidence for surrounding material in an envelope in addition to a
circumstellar disk. In these cases, we show that accretion shock heating is a
plausible excitation mechanism. The detected emission lines are narrow (~10
km/s), centered at the stellar velocity, and spatially unresolved at scales of
0.4 arcsec, which is consistent with origin from a disk at radii 10-50 AU from
the star. In cases where we detect multiple emission lines, we derive
temperatures > 500 K from ~1 M_earth of gas. Our upper limits for the
non-detections place upper limits on the amount of H2 gas with T > 500 K of
less than a few Earth masses. Such warm gas temperatures are significantly
higher than the equilibrium dust temperatures at these radii, suggesting that
the gas is decoupled from the dust in the regions we are studying and that
processes such as UV, X-ray, and accretion heating may be important.Comment: 24 pages, 16 figures, 5 tables, ApJ accepte
Disks and Outflows in CO Rovibrational Emission from Embedded, Low-Mass Young Stellar Objects
Young circumstellar disks that are still embedded in dense molecular
envelopes may differ from their older counterparts, but are historically
difficult to study because emission from a disk can be confused with envelope
or outflow emission. CO fundamental emission is a potentially powerful probe of
the disk/wind structure within a few AU of young protostars. In this paper, we
present high spectral (R=90,000) and spatial (0.3") resolution VLT/CRIRES
M-band spectra of 18 low-mass young stellar objects (YSOs) with dense envelopes
in nearby star-froming regions to explore the utility of CO fundamental 4.6
micron emission as a probe of very young disks. CO fundamental emission is
detected from 14 of the YSOs in our sample. The emission line profiles show a
range of strengths and shapes, but can generally be classified into a broad,
warm component and a narrow, cool component. The broad CO emission is detected
more frequently from YSOs with bolometric luminosities of <15 Lsun than those
with >15 Lsun, and as with CO emission from CTTSs is attributed to the warm
(~1000 K) inner AU of the disk. The CO emission from objects with high
bolometric luminosity is produced in cooler (~320 K), narrow lines in 12CO and
in rarer isotopologues. From some objects, the narrow lines are blueshifted by
up to ~10 km/s, indicating a slow wind origin. For other sources the lines are
located at the systemic velocity of the star and likely arise in the disk. For
a few YSOs, spatially-extended CO and H2 S(9) emission is detected up to 2"
from the central source and is attributed to interactions between the wind and
surrounding molecular material. Warm CO absorption is detected in the wind of
six objects with velocities up to 100 km/s, often in discrete velocity
components. That the wind is partially molecular where it is launched favors
ejection in a disk wind rather than a coronal or chromospheric wind.Comment: 26 pages, accepted by A&
The AIROPA software package - Milestones for testing general relativity in the strong gravity regime with AO
General relativity can be tested in the strong gravity regime by monitoring stars orbiting the supermassive black hole at the Galactic Center with adaptive optics. However, the limiting source of uncertainty is the spatial PSF variability due to atmospheric anisoplanatism and instrumental aberrations. The Galactic Center Group at UCLA has completed a project developing algorithms to predict PSF variability for Keck AO images. We have created a new software package (AIROPA), based on modified versions of StarFinder and Arroyo, that takes atmospheric turbulence profiles, instrumental aberration maps, and images as inputs and delivers improved photometry and astrometry on crowded fields. This software package will be made publicly available soon
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Measuring physical properties of pre-main sequence stars using high resolution infrared spectroscopy
textPhysical properties of pre–main sequence stars and their disks are measured
from high resolution near–infrared spectra. A new fitting technique using spectral
synthesis models has been developed to find the best fit to fully resolved K band
absorption lines, allowing measurements of the stellar effective temperature, rate
of rotation, and amount of non–stellar continuum excess from infrared emission
by the circumstellar disk. An IDL fitting routine selects the best spectral synthesis
model by the RMS minimum to the residuals of the fits, and has been validated by
observations of MK standards. This new technique has been applied to a sample
of pre–main sequence stars in the ρ Ophiuchi dark cloud to obtain accurate effective
temperatures, continuum veilings, and some of the first measurements of vsini
rotations in highly extincted young stars from 2.2 µm spectra. In two sources, a
new spectroscopic technique to measure surface gravity has been applied using line
flux ratios in high resolution spectra at 2.2 µm and 2.3 µm, leading to the first luminosity
measurements that are independent of extinction and only weakly dependent
on continuum excess. Previous assumptions of no continuum excess at J (1.2 µm)
upon which the photometrically determined luminosities are based, are called into
question with these new results. In the absence of strong magnetic fields, the ages
of these objects inferred from stellar evolutionary model tracks on the HR diagram
reveals an older age (6–9 Myr) from spectroscopically determined luminosities than
from the photometry of the same objects.
Another useful application of high resolution spectroscopy is the detection
of binary systems. Characterization of binary systems offers a direct way to obtain
mass and relative mass information. With a sensitivity down to ~0.5 km s-1
, we
have measured precision radial velocities of the sources in our Ophiuchus sample,
resulting in the discovery of one short period (P <
1 yr) pre–main sequence binary
(GSS29). This system has been subsequently monitored to determine its orbital
characteristics (P = 145 d, v2 = 29 km s -1
) and constrain the mass (M1 + M2
~1.8 M⊙ ). We find the dominant spectral line component to be the less massive (and
cooler) star. The more massive star is mostly featureless because it is hotter and
rotating fast. More observations are required to better constrain these preliminary
results.Astronom
High-Resolution Spectroscopy Of Ne II Emission From AA Tau And GM Aur
We present high-resolution (R = 80,000) spectroscopy of [Ne II] emission from two young stars, GM Aur and AA Tau, which have moderate to high inclinations. The emission from both sources appears centered near the stellar velocity and is broader than the [Ne II] emission measured previously for the face-on disk system TW Hya. These properties are consistent with a disk origin for the [Ne II] emission we detect, with disk rotation (rather than photoevaporation or turbulence in a hot disk atmosphere) playing the dominant role in the origin of the line width. In the non-face-on systems, the [Ne II] emission is narrower than the CO fundamental emission from the same sources. If the widths of both diagnostics are dominated by Keplerian rotation, this suggests that the [Ne II] emission arises from larger disk radii on average than does the CO emission. The equivalent width of the [Ne II] emission we detect is less than that of the spectrally unresolved [Ne II] feature in the Spitzer spectra of the same sources. Variability in the [Ne II] emission or the mid-infrared continuum, a spatially extended [Ne II] component, or a very (spectrally) broad [Ne II] component might account for the difference in the equivalent widths.NSF AST-0607312, AST-0708074NASA/USRA SOFIAGemini ObservatoryNASA NNH07AG51I, NNG04GG92GNASA Astrobiology Institute under Cooperative Agreement CAN-02-OSS-02Life and Planets Astrobiology Center (LAPLACE)6.1 baseAssociation of Universities for Research in Astronomy, Inc.Cooperative agreement with the NSF on behalf of the Gemini partnershipParticle Physics and Astronomy Research Council (United Kingdom)National Research Council (Canada)CONICYT (Chile)Australian Research Council (Australia)CNPq (Brazil)CONICET (Argentina)W.M. Keck FoundationAstronom
First Comet Observations with NIRSPEC-2 at Keck: Outgassing Sources of Parent Volatiles and Abundances Based on Alternative Taxonomic Compositional Baselines in 46P/Wirtanen
International audienceA major upgrade to the NIRSPEC instrument at the Keck II telescope was successfully completed in time for near-infrared spectroscopic observations of comet 46P/Wirtanen during its exceptionally close flyby of Earth in 2018 December. These studies determined the abundances of several volatiles, including C2H2, C2H6, CH3OH, NH3, HCN, H2CO, and H2O. Long-slit spatial distributions of gas rotational temperature and column density are diagnostic for the presence of icy grains in the coma and understanding if different volatiles are associated with common or distinct outgassing sources. These spatial distributions suggest that C2H2, C2H6, and HCN have a common outgassing source, whereas H2O and CH3OH have additional, more extended sources. The synergy of these findings with observations by space missions (Rosetta and EPOXI) motivates continuing studies to address whether or not C2H6, C2H2, and HCN have a common source of release (plausibly associated with CO2) in a larger sample of comets and whether systematic differences exist in the release of these species compared to H2O and CH3OH. Abundances of volatiles are reported relative to H2O, as traditionally done, as well as C2H6. While not unique, the choice of C2H6 demonstrates the value of extending the chemical taxonomy of parent volatiles in comets toward additional compositional "baselines" and, importantly, closer integration between coma abundances and the underlying volatile associations as revealed by spatial distributions. Our findings on composition and sources of outgassing include information relevant to future evaluations of 46P/Wirtanen as a prospective spacecraft target