391 research outputs found
Development and testing of a graphical FORTRAN learning tool for novice programmers
To address the difficulties associated with computer programming, this article first looks at some reasons why students, especially engineering students, find programming such a daunting prospect, and it proposes a programming learning tool managed by a Deterministic Finite Automaton (DFA). The DFA machine used a graphical environment provided by Simulink to teach the FOR-mula TRANslator (FORTRAN) programming language to science students. The proposed programming learning tool and the traditional method of teaching were compared and evaluated. The results of evaluation indicated that there was an improvement in learning effectiveness of the proposed learning tool
Overview of the spectrometer optical fiber feed for the Habitable-zone Planet Finder
The Habitable-zone Planet Finder (HPF) is a highly stabilized fiber fed
precision radial velocity (RV) spectrograph working in the Near Infrared (NIR):
810 - 1280 nm . In this paper we present an overview of the preparation of the
optical fibers for HPF. The entire fiber train from the telescope focus down to
the cryostat is detailed. We also discuss the fiber polishing, splicing and its
integration into the instrument using a fused silica puck. HPF was designed to
be able to operate in two modes, High Resolution (HR- the only mode mode
currently commissioned) and High Efficiency (HE). We discuss these fiber heads
and the procedure we adopted to attach the slit on to the HR fibers.Comment: Presented at 2018 SPIE Astronomical Telescopes + Instrumentation,
Austin, Texas, USA. 18 pages, 25 figures, and 2 table
Solar Contamination in Extreme-precision Radial-velocity Measurements: Deleterious Effects and Prospects for Mitigation
Solar contamination, due to moonlight and atmospheric scattering of sunlight, can cause systematic errors in stellar radial velocity (RV) measurements that significantly detract from the ~10 cm s−1 sensitivity required for the detection and characterization of terrestrial exoplanets in or near habitable zones of Sun-like stars. The addition of low-level spectral contamination at variable effective velocity offsets introduces systematic noise when measuring velocities using classical mask-based or template-based cross-correlation techniques. Here we present simulations estimating the range of RV measurement error induced by uncorrected scattered sunlight contamination. We explore potential correction techniques, using both simultaneous spectrometer sky fibers and broadband imaging via coherent fiber imaging bundles, that could reliably reduce this source of error to below the photon-noise limit of typical stellar observations. We discuss the limitations of these simulations, the underlying assumptions, and mitigation mechanisms. We also present and discuss the components designed and built into the NEID (NN-EXPLORE Exoplanet Investigations with Doppler spectroscopy) precision RV instrument for the WIYN 3.5 m telescope, to serve as an ongoing resource for the community to explore and evaluate correction techniques. We emphasize that while "bright time" has been traditionally adequate for RV science, the goal of 10 cm s−1 precision on the most interesting exoplanetary systems may necessitate access to darker skies for these next-generation instruments
Constrained modelling of instrumental radial velocity drift in precision Radial Velocity Spectrometers: Application to HPF
For precise measurement of the radial velocity change in a star, the precision of the wavelength solution is 4 orders more important than accuracy of the wavelength solution. Since the absolute wavelength solution model of a multi-order echelle spectrographs require a large number of parameters, it is better to track the change in wavelength solution over time instead of refitting the complete wavelength solution without any constrains. For stabilized spectrographs like The Habitable-Zone Planet Finder (HPF) and NEID, these changes in wavelength solution are significantly low order and can be modeled with only a few parameters. Table 1, shows an example of low order changes to dispersion solution we expect from various physical mechanisms in HPF or NEID
Persistent starspot signals on M dwarfs: multi-wavelength Doppler observations with the Habitable-zone Planet Finder and Keck/HIRES
Young, rapidly-rotating M dwarfs exhibit prominent starspots, which create
quasiperiodic signals in their photometric and Doppler spectroscopic
measurements. The periodic Doppler signals can mimic radial velocity (RV)
changes expected from orbiting exoplanets. Exoplanets can be distinguished from
activity-induced false positives by the chromaticity and long-term incoherence
of starspot signals, but these qualities are poorly constrained for
fully-convective M stars. Coherent photometric starspot signals on M dwarfs may
persist for hundreds of rotations, and the wavelength dependence of starspot RV
signals may not be consistent between stars due to differences in their
magnetic fields and active regions. We obtained precise multi-wavelength RVs of
four rapidly-rotating M dwarfs (AD Leo, G 227-22, GJ 1245B, GJ 3959) using the
near-infrared (NIR) Habitable-zone Planet Finder, and the optical Keck/HIRES
spectrometer. Our RVs are complemented by photometry from Kepler, TESS, and the
Las Cumbres Observatory (LCO) network of telescopes. We found that all four
stars exhibit large spot-induced Doppler signals at their rotation periods, and
investigated the longevity and optical-to-NIR chromaticity for these signals.
The phase curves remain coherent much longer than is typical for Sunlike stars.
Their chromaticity varies, and one star (GJ 3959) exhibits optical and NIR RV
modulation consistent in both phase and amplitude. In general, though, we find
that the NIR amplitudes are lower than their optical counterparts. We conclude
that starspot modulation for rapidly-rotating M stars frequently remains
coherent for hundreds of stellar rotations, and gives rise to Doppler signals
that, due to this coherence, may be mistaken for exoplanets.Comment: Accepted for publication in the Astrophysical Journa
Impact of crosshatch patterns in H2RGs on high-precision radial velocity measurements: exploration of measurement and mitigation paths with the Habitable-Zone Planet Finder
Teledyne’s H2RG detector images suffer from crosshatch like patterns, which arise from subpixel quantum efficiency (QE) variation. We present our measurements of this subpixel QE variation in the Habitable-Zone Planet Finder’s H2RG detector. We present a simple model to estimate the impact of subpixel QE variations on the radial velocity and how a first-order correction can be implemented to correct for the artifact in the spectrum. We also present how the HPF’s future upgraded laser frequency comb will enable us to implement this correction
The Epoch of Giant Planet Migration Planet Search Program. I. Near-Infrared Radial Velocity Jitter of Young Sun-like Stars
We present early results from the Epoch of Giant Planet Migration program, a
precise RV survey of over one hundred intermediate-age (20200 Myr) G
and K dwarfs with the Habitable-Zone Planet Finder spectrograph (HPF) at
McDonald Observatory's Hobby-Eberly Telescope (HET). The goals of this program
are to determine the timescale and dominant physical mechanism of giant planet
migration interior to the water ice line of Sun-like stars. Here, we summarize
results from the first 14 months of this program, with a focus on our custom RV
pipeline for HPF, a measurement of the intrinsic near-infrared RV activity of
young Solar analogs, and modeling the underlying population-level distribution
of stellar jitter. We demonstrate on-sky stability at the sub-2 m s
level for the K2 standard HD 3765 using a least-squares matching method to
extract precise RVs. Based on a subsample of 29 stars with at least three RV
measurements from our program, we find a median RMS level of 34 m s.
This is nearly a factor of 2 lower than the median RMS level in the optical of
60 m s for a comparison sample with similar ages and spectral types as
our targets. The observed near-infrared jitter measurements for this subsample
are well reproduced with a log-normal parent distribution with and
. Finally, by compiling RMS values from previous planet search
programs, we show that near-infrared jitter for G and K dwarfs generally decays
with age in a similar fashion to optical wavelengths, albeit with a shallower
slope and lower overall values for ages 1 Gyr
Impact of crosshatch patterns in H2RGs on high-precision radial velocity measurements: exploration of measurement and mitigation paths with the Habitable-Zone Planet Finder
Teledyne’s H2RG detector images suffer from crosshatch like patterns, which arise from subpixel quantum efficiency (QE) variation. We present our measurements of this subpixel QE variation in the Habitable-Zone Planet Finder’s H2RG detector. We present a simple model to estimate the impact of subpixel QE variations on the radial velocity and how a first-order correction can be implemented to correct for the artifact in the spectrum. We also present how the HPF’s future upgraded laser frequency comb will enable us to implement this correction
Long-term operation of a laser frequency comb with the Habitable Zone Planet Finder
Laser frequency combs are an ideal calibration source for precision astronomical spectrographs. We report on the demonstrated long term operation of a laser frequency comb that we designed and built as the primary calibrator for the Habitable Zone Planet Finder (HPF). The core technology of the comb is based on robust, polarization maintaining fiber coupled electro-optic modulators and broadband supercontinuum generation spanning 700-1600 nm in an efficient silicon nitride waveguide. The comb is continuously maintained on and ready to use, and since May 2018 the laser frequency comb has had a total uptime of 97%
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