87 research outputs found
Near field modal noise reduction using annealed optical fiber
Incomplete and unstable mode population has long complicated the application of optical fiber for transferring star and calibration light to high precision spectrographs. The need for improved precision calibrators in support of radial velocity planet surveys has led to the introduction of coherent wavelengths sources using single mode fibers that are then coupled into multi-mode fibers, further exacerbating this problem. We explore mode scrambling in annealed optical fiber with and without agitation, as compared to that obtained using octagonal fiber and using an integrating sphere. We observe improved scrambling with annealed fibers compared to conventional and octagonal fibers
Precision near-infrared radial velocity instrumentation II: Non-Circular Core Fiber Scrambler
We have built and commissioned a prototype agitated non-circular core fiber
scrambler for precision spectroscopic radial velocity measurements in the
near-infrared H band. We have collected the first on-sky performance and modal
noise tests of these novel fibers in the near-infrared at H and K bands using
the CSHELL spectrograph at the NASA InfraRed Telescope Facility (IRTF). We
discuss the design behind our novel reverse injection of a red laser for
co-alignment of star-light with the fiber tip via a corner cube and visible
camera. We summarize the practical details involved in the construction of the
fiber scrambler, and the mechanical agitation of the fiber at the telescope. We
present radial velocity measurements of a bright standard star taken with and
without the fiber scrambler to quantify the relative improvement in the
obtainable blaze function stability, the line spread function stability, and
the resulting radial velocity precision. We assess the feasibility of applying
this illumination stabilization technique to the next generation of
near-infrared spectrographs such as iSHELL on IRTF and an upgraded NIRSPEC at
Keck. Our results may also be applied in the visible for smaller core diameter
fibers where fiber modal noise is a significant factor, such as behind an
adaptive optics system or on a small < 1 meter class telescope such as is being
pursued by the MINERVA and LCOGT collaborations.Comment: Proceedings of the SPIE Optics and Photonics Conference "Techniques
and Instrumentation for Detection of Exoplanets VI" held in San Diego, CA,
August 25-29, 201
Potential Drivers of Mid-Infrared Variability in Young Stars: Testing Physical Models with Multiepoch Near-Infrared Spectra of YSOs in ρ Oph
Recent studies have identified several young stellar objects (YSOs) which exhibit significant mid-infrared (mid-IR) variability. A wide range of physical mechanisms may be responsible for these variations, including changes in a YSO’s accretion rate or in the extinction or emission from the inner disk. We have obtained and analyzed multiepoch near-infrared (NIR) spectra for five actively accreting YSOs in the ρ Oph star-forming region along with contemporaneous mid-IR light curves obtained as part of the YSOVAR Spitzer/IRAC survey. Four of the five YSOs exhibit mid-IR light curves with modest (∼0.2–0.4 mag) but statistically significant variations over our 40-day observation window. Measuring the strengths of prominent photospheric absorption lines and accretion sensitive H I and He I lines in each NIR spectrum, we derive estimates of each YSO’s spectral type, effective temperature (T_eff), and H-band extinction (A_H), and analyze the time evolution of their NIR veiling (r_H and r_K) and mass accretion rates (Ṁ_acc). Defining a YSO’s evolutionary stage such that heavily veiled, high accretion rate objects are less evolved than those with lower levels of veiling and ongoing accretion, we infer that GY 314 is the most evolved YSO in our sample, with GY 308 and GY 292 at progressively earlier evolutionary stages. Leveraging our multiepoch, multiwavelength dataset, we detect significant variations in mass accretion rates over timescales of days to weeks, but find that extinction levels in these YSOs remain relatively constant. We find no correlation between these YSO mid-IR light curves and time-resolved veiling or mass accretion rates, such that we are unable to link their mid-IR variability with physical processes localized near the inner edge of the circumstellar disk or within regions which are directly responsive to mass accretion. We do find, however, that redshifted He I λ10830 emission, where present in our spectra, shows both quantitative and qualitative temporal correlations with accretion-sensitive H I emission lines. Blueshifted He I absorption, on the other hand, does not demonstrate a similar correlation, although the time-averaged strength of this blueshifted absorption is correlated with the time-averaged accretion rate in our sample of YSOs
Design and Construction of Absorption Cells for Precision Radial Velocities in the K Band using Methane Isotopologues
We present a method to optimize absorption cells for precise wavelength
calibration in the near-infrared. We apply it to design and optimize methane
isotopologue cells for precision radial velocity measurements in the K band. We
also describe the construction and installation of two such cells for the
CSHELL spectrograph at NASA's IRTF. We have obtained their high-resolution
laboratory spectra, which we can then use in precision radial velocity
measurements and which can also have other applications. In terms of obtainable
RV precision methane should out-perform other proposed cells, such as the
ammonia cell (NH) recently demonstrated on CRIRES/VLT. The
laboratory spectra of Ammonia and the Methane cells show strong absorption
features in the H band that could also be exploited for precision Doppler
measurements. We present spectra and preliminary radial velocity measurements
obtained during our first-light run. These initial results show that a
precision down to 20-30 m s can be obtained using a wavelength interval
of only 5 nm in the K band and S/N150. This supports the prediction that
a precision down to a few m s can be achieved on late M dwarfs using the
new generation of NIR spectrographs, thus enabling the detection of terrestrial
planets in their habitable zones. Doppler measurements in the NIR can also be
used to mitigate the radial velocity jitter due to stellar activity enabling
more efficient surveys on young active stars.Comment: accepted PASP, Apr 2012 (in press). Preprint version with 36 pages, 9
Figures, 2 Table
Design, motivation, and on-sky tests of an efficient fiber coupling unit for 1-meter class telescopes
We present the science motivation, design, and on-sky test data of a high-throughput fiber coupling unit suitable for automated 1-meter class telescopes. The optical and mechanical design of the fiber coupling is detailed and we describe a flexible controller software designed specifically for this unit. The system performance is characterized with a set of numerical simulations, and we present on-sky results that validate the performance of the controller and the expected throughput of the fiber coupling. This unit was designed specifically for the MINERVA array, a robotic observatory consisting of multiple 0.7 m telescopes linked to a single high-resolution stabilized spectrograph for the purpose of exoplanet discovery using high-cadence radial velocimetry. However, this unit could easily be used for general astronomical purposes requiring fiber coupling or precise guiding
An Unusual Transmission Spectrum for the Sub-Saturn KELT-11b Suggestive of a Sub-Solar Water Abundance
We present an optical-to-infrared transmission spectrum of the inflated
sub-Saturn KELT-11b measured with the Transiting Exoplanet Survey Satellite
(TESS), the Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectroscopic
grism, and the Spitzer Space Telescope (Spitzer) at 3.6 m, in addition to
a Spitzer 4.5 m secondary eclipse. The precise HST transmission spectrum
notably reveals a low-amplitude water feature with an unusual shape. Based on
free retrieval analyses with varying molecular abundances, we find strong
evidence for water absorption. Depending on model assumptions, we also find
tentative evidence for other absorbers (HCN, TiO, and AlO). The retrieved water
abundance is generally solar (0.001--0.7 solar
over a range of model assumptions), several orders of magnitude lower than
expected from planet formation models based on the solar system metallicity
trend. We also consider chemical equilibrium and self-consistent 1D
radiative-convective equilibrium model fits and find they too prefer low
metallicities (, consistent with the free retrieval
results). However, all the retrievals should be interpreted with some caution
since they either require additional absorbers that are far out of chemical
equilibrium to explain the shape of the spectrum or are simply poor fits to the
data. Finally, we find the Spitzer secondary eclipse is indicative of full heat
redistribution from KELT-11b's dayside to nightside, assuming a clear dayside.
These potentially unusual results for KELT-11b's composition are suggestive of
new challenges on the horizon for atmosphere and formation models in the face
of increasingly precise measurements of exoplanet spectra.Comment: Accepted to The Astronomical Journal. 31 pages, 20 figures, 7 table
JWST/NIRCam Coronagraphy of the Young Planet-hosting Debris Disk AU Microscopii
High-contrast imaging of debris disk systems permits us to assess the
composition and size distribution of circumstellar dust, to probe recent
dynamical histories, and to directly detect and characterize embedded
exoplanets. Observations of these systems in the infrared beyond 2--3 m
promise access to both extremely favorable planet contrasts and numerous
scattered-light spectral features -- but have typically been inhibited by the
brightness of the sky at these wavelengths. We present coronagraphy of the AU
Microscopii (AU Mic) system using JWST's Near Infrared Camera (NIRCam) in two
filters spanning 3--5 m. These data provide the first images of the
system's famous debris disk at these wavelengths and permit additional
constraints on its properties and morphology. Conducting a deep search for
companions in these data, we do not identify any compelling candidates.
However, with sensitivity sufficient to recover planets as small as
Jupiter masses beyond ( au) with
confidence, these data place significant constraints on any massive companions
that might still remain at large separations and provide additional context for
the compact, multi-planet system orbiting very close-in. The observations
presented here highlight NIRCam's unique capabilities for probing similar disks
in this largely unexplored wavelength range, and provide the deepest direct
imaging constraints on wide-orbit giant planets in this very well studied
benchmark system.Comment: 27 pages, 14 figure
A dense mini-Neptune orbiting the bright young star HD 18599
© 2022 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1093/mnras/stac2845Very little is known about the young planet population because the detection of small planets orbiting young stars is obscured by the effects of stellar activity and fast rotation which mask planets within radial velocity and transit data sets. The few planets that have been discovered in young clusters generally orbit stars too faint for any detailed follow-up analysis. Here we present the characterization of a new mini-Neptune planet orbiting the bright (V=9) and nearby K2 dwarf star, HD 18599. The planet candidate was originally detected in TESS light curves from Sectors 2, 3, 29, and 30, with an orbital period of 4.138~days. We then used HARPS and FEROS radial velocities, to find the companion mass to be 25.54.6~M. When we combine this with the measured radius from TESS, of 2.700.05~R, we find a high planetary density of 7.11.4~g cm. The planet exists on the edge of the Neptune Desert and is the first young planet (300 Myr) of its type to inhabit this region. Structure models argue for a bulk composition to consist of 23% HO and 77% Rock and Iron. Future follow-up with large ground- and space-based telescopes can enable us to begin to understand in detail the characteristics of young Neptunes in the galaxy.Peer reviewe
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