16 research outputs found
Pyodine: An open, flexible reduction software for iodine-calibrated precise radial velocities
For existing and future projects dedicated to measuring precise radial
velocities (RVs), we have created an open-source, flexible data reduction
software to extract RVs from \'echelle spectra via the iodine (I)
absorption cell method. The software, called , is completely written
in Python and has been built in a modular structure to allow for easy
adaptation to different instruments. We present the fundamental concepts
employed by , which build on existing I reduction codes, and give
an overview of the software's structure. We adapted to two
instruments, Hertzsprung SONG located at Teide Observatory (SONG hereafter) and
the Hamilton spectrograph at Lick Observatory (Lick hereafter), and demonstrate
the code's flexibility and its performance on spectra from these facilities.
Both for SONG and Lick data, the results generally match the RV
precision achieved by the dedicated instrument pipelines. Notably, our code
reaches a precision of roughly on a short-term solar time
series of SONG spectra, and confirms the planet-induced RV variations of the
star HIP~36616 on spectra from SONG and Lick. Using the solar spectra, we also
demonstrate the capabilities of our software in extracting velocity time series
from single absorption lines. A probable instrumental effect of SONG is still
visible in the RVs, despite being a bit damped as compared to the
original results. With we prove the feasibility of a highly precise,
yet instrument-flexible I reduction software, and in the future the code
will be part of the dedicated data reduction pipelines for the SONG network and
the Waltz telescope project in Heidelberg.Comment: Published in Astronomy & Astrophysics, 13 pages, 8 figure
Photon-weighted barycentric correction and its importance for precise radial velocities
When applying the barycentric correction to a precise radial velocity
measurement, it is common practice to calculate its value only at the
photon-weighted midpoint time of the observation instead of integrating over
the entire exposure. However, since the barycentric correction does not change
linearly with time, this leads to systematic errors in the derived radial
velocities. The typical magnitude of this second-order effect is of order 10 cm
s, but it depends on several parameters, e.g. the latitude of the
observatory, the position of the target on the sky, and the exposure time. We
show that there are realistic observing scenarios, where the errors can amount
to more than 1 ms. We therefore recommend that instruments operating in
this regime always record and store the exposure meter flux curve (or a similar
measure) to be used as photon-weights for the barycentric correction. In
existing data, if the flux curve is no longer available, we argue that
second-order errors in the barycentric correction can be mitigated by adding a
correction term assuming constant flux.Comment: 9 pages, 7 figures, accepted to MNRA
An Extreme Precision Radial Velocity Pipeline: First Radial Velocities from EXPRES
The EXtreme PREcision Spectrograph (EXPRES) is an environmentally stabilized,
fiber-fed, , optical spectrograph. It was recently commissioned at
the 4.3-m Lowell Discovery Telescope (LDT) near Flagstaff, Arizona. The
spectrograph was designed with a target radial-velocity (RV) precision of
30. In addition to instrumental innovations, the EXPRES
pipeline, presented here, is the first for an on-sky, optical, fiber-fed
spectrograph to employ many novel techniques---including an "extended flat"
fiber used for wavelength-dependent quantum efficiency characterization of the
CCD, a flat-relative optimal extraction algorithm, chromatic barycentric
corrections, chromatic calibration offsets, and an ultra-precise laser
frequency comb for wavelength calibration. We describe the reduction,
calibration, and radial-velocity analysis pipeline used for EXPRES and present
an example of our current sub-meter-per-second RV measurement precision, which
reaches a formal, single-measurement error of 0.3 for an
observation with a per-pixel signal-to-noise ratio of 250. These velocities
yield an orbital solution on the known exoplanet host 51 Peg that matches
literature values with a residual RMS of 0.895
A Giant Planet Candidate Transiting a White Dwarf
Astronomers have discovered thousands of planets outside the solar system,
most of which orbit stars that will eventually evolve into red giants and then
into white dwarfs. During the red giant phase, any close-orbiting planets will
be engulfed by the star, but more distant planets can survive this phase and
remain in orbit around the white dwarf. Some white dwarfs show evidence for
rocky material floating in their atmospheres, in warm debris disks, or orbiting
very closely, which has been interpreted as the debris of rocky planets that
were scattered inward and tidally disrupted. Recently, the discovery of a
gaseous debris disk with a composition similar to ice giant planets
demonstrated that massive planets might also find their way into tight orbits
around white dwarfs, but it is unclear whether the planets can survive the
journey. So far, the detection of intact planets in close orbits around white
dwarfs has remained elusive. Here, we report the discovery of a giant planet
candidate transiting the white dwarf WD 1856+534 (TIC 267574918) every 1.4
days. The planet candidate is roughly the same size as Jupiter and is no more
than 14 times as massive (with 95% confidence). Other cases of white dwarfs
with close brown dwarf or stellar companions are explained as the consequence
of common-envelope evolution, wherein the original orbit is enveloped during
the red-giant phase and shrinks due to friction. In this case, though, the low
mass and relatively long orbital period of the planet candidate make
common-envelope evolution less likely. Instead, the WD 1856+534 system seems to
demonstrate that giant planets can be scattered into tight orbits without being
tidally disrupted, and motivates searches for smaller transiting planets around
white dwarfs.Comment: 50 pages, 12 figures, 2 tables. Published in Nature on Sept. 17,
2020. The final authenticated version is available online at:
https://www.nature.com/articles/s41586-020-2713-
Exoplanet atmospheres at high resolution through a modest-size telescope : FeII in MASCARA-2b and KELT-9b with FIES on the Nordic Optical Telescope
Ground-based, high-resolution spectrographs are providing us with an unprecedented view of the dynamics and chemistry of the atmospheres of planets outside the Solar System. While there are a large number of stable and precise high-resolution spectrographs on modest-size telescopes, it is the spectrographs at observatories with apertures larger than 3.5 m that dominate the atmospheric follow-up of exoplanets. In this work we explore the potential of characterising exoplanetary atmospheres with FIES, a high-resolution spectrograph at the 2.56 m Nordic Optical Telescope. We observed two transits of MASCARA-2 b (also known as KELT-20 b) and one transit of KELT-9 b to search for atomic iron, a species that has recently been discovered in both neutral and ionised forms in the atmospheres of these ultra-hot Jupiters using large telescopes. Using a cross-correlation method, we detect a signal of FeII at the 4.5and 4.0level in the transits of MaSCARA-2 b. We also detect FeII in the transit of KELT-9 b at the 8.5level. Although we do not find any significant Doppler shift in the signal of MASCARA-2 b, we do measure a moderate blueshift (3a-6 km s1) of the feature in KELT-9 b, which might be a manifestation of high-velocity winds transporting FeII from the planetary dayside to the nightside. Our work demonstrates the feasibility of investigating exoplanet atmospheres with FIES, and it potentially unlocks a wealth of additional atmosphere detections with this and other high-resolution spectrographs mounted on similar-size telescopes
High-resolution transmission spectroscopy of MASCARA-2 b with EXPRES
We report detections of atomic species in the atmosphere of MASCARA-2 b, using the first transit observations obtained with the newly commissioned EXPRES spectrograph. EXPRES is a highly stabilized optical echelle spectrograph, designed to detect stellar reflex motions with amplitudes down to 30 cm s−1, and has recently been deployed at the Lowell Discovery Telescope. By analyzing the transmission spectrum of the ultra-hot Jupiter MASCARA-2 b using the cross-correlation method, we confirm previous detections of Fe I, Fe II, and Na I, which likely originate in the upper regions of the inflated atmosphere. In addition, we report significant detections of Mg I and Cr II. The absorption strengths change slightly with time, possibly indicating different temperatures and chemistry in the day- and nightside terminators. Using the effective stellar line-shape variation induced by the transiting planet, we constrain the projected spin-orbit misalignment of the system to 1.6 ± 3.1 degrees, consistent with an aligned orbit. We demonstrate that EXPRES joins a suite of instruments capable of phase-resolved spectroscopy of exoplanet atmospheres
Vitality of Gorse-seed
The EXtreme PREcision Spectrograph (EXPRES) is a new Doppler spectrograph designed to reach a radial-velocity measurement precision sufficient to detect Earth-like exoplanets orbiting nearby, bright stars. We report on extensive laboratory testing and on-sky observations to quantitatively assess the instrumental radial-velocity measurement precision of EXPRES, with a focused discussion of individual terms in the instrument error budget. We find that EXPRES can reach a single-measurement instrument calibration precision better than 10 cm s-1, not including photon noise from stellar observations. We also report on the performance of the various environmental, mechanical, and optical subsystems of EXPRES, assessing any contributions to radial-velocity error. For atmospheric and telescope related effects, this includes the fast tip-tilt guiding system, atmospheric dispersion compensation, and the chromatic exposure meter. For instrument calibration, this includes the laser fRequency comb (LFC), flat-field light source, CCD detector, and effects in the optical fibers. Modal noise is mitigated to a negligible level via a chaotic fiber agitator, which is especially important for wavelength calibration with the LFC. Regarding detector effects, we empirically assess the impact on the radial-velocity precision due to pixel-position nonuniformities and charge transfer inefficiency (CTI). EXPRES has begun its science survey to discover exoplanets orbiting G-dwarf and K-dwarf stars, in addition to transit spectroscopy and measurements of the Rossiter-McLaughlin effect. © 2020. The American Astronomical Society. All rights reserved.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Confirmation and characterisation of three giant planets detected by TESS from the FIES/NOT and Tull/McDonald spectrographs
We report the confirmation and characterisation of TOI-1820 b, TOI-2025 b, and TOI-2158 b, three Jupiter-sized planets on short-period orbits around G-type stars detected by TESS. Through our ground-based efforts using the FIES and Tull spectrographs, we have confirmed these planets and characterised their orbits, and find periods of around 4.9 d, 8.9 d, and 8.6 d for TOI-1820 b, TOI-2025 b, and TOI-2158 b, respectively. The sizes of the planets range from 0.96 to 1.14 Jupiter radii, and their masses are in the range from 0.8 to 4.4 Jupiter masses. For two of the systems, namely TOI-2025 and TOI-2158, we see a long-term trend in the radial velocities, indicating the presence of an outer companion in each of the two systems. For TOI-2025 we furthermore find the star to be well aligned with the orbit, with a projected obliquity of 9−31+33°. As these planets are all found in relatively bright systems (V ~ 10.9–11.6 mag), they are well suited for further studies, which could help shed light on the formation and migration of hot and warm Jupiters