15 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
In search of gravity mode signatures in main sequence solar-type stars observed by Kepler
Gravity modes (g modes), mixed gravito-acoustic modes (mixed modes), and
gravito-inertial modes (gi modes) possess unmatched properties as probes for
stars with radiative interiors. The structural and dynamical constraints that
they are able to provide cannot be accessed by other means. While they provide
precious insights into the internal dynamics of evolved stars as well as
massive and intermediate-mass stars, their non-detection in main sequence (MS)
solar-type stars make them a crucial missing piece in our understanding of
angular momentum transport in radiative zones and stellar rotational evolution.
In this work, we aim to apply certain analysis tools originally developed for
helioseismology in order to look for g-mode signatures in MS solar-type stars.
We select a sample of the 34 most promising MS solar-type stars with Kepler
four-year long photometric time series. All these stars are well-characterised
late F-type stars with thin convective envelopes, fast convective flows, and
stochastically excited acoustic modes (p modes). For each star, we compute the
background noise level of the Fourier power spectrum to identify significant
peaks at low frequency. After successfully detecting individual peaks in 12
targets, we further analyse four of them and observe distinct patterns of
surrounding peaks with a low probability of being noise artifacts. Comparisons
with the predictions from reference models suggest that these patterns are
compatible with the presence of non-asymptotic low-order pure g modes, pure p
modes, and mixed modes. Given their sensitivity to both the convective core
interface stratification and the coupling between p- and g-mode resonant
cavities, such modes are able to provide strong constraints on the structure
and evolutionary states of the related targets. [abridged]Comment: 19 pages, 19 figures, accepted for publication in A&
Precise radial velocities of giant stars XV. Mysterious nearly periodic radial velocity variations in the eccentric binary Cygni
Using the Hamilton Echelle Spectrograph at Lick Observatory, we have obtained
precise radial velocities (RVs) of a sample of 373 G- and K-giant stars over
more than 12 years, leading to the discovery of several single and multiple
planetary systems. The RVs of the long-period (~53 years) spectroscopic binary
Cyg (HIP 102488) are found to exhibit additional regular variations
with a much shorter period (~291 days). We intend to improve the orbital
solution of the Cyg system and attempt to identify the cause of the
nearly periodic shorter period variations, which might be due to an additional
substellar companion. We used precise RV measurements of the K-giant star
Cyg from Lick Observatory, in combination with a large set of RVs
collected more recently with the SONG telescope, as well as archival data sets.
Our Keplerian model to the RVs characterizes the orbit of the spectroscopic
binary to higher precision than achieved previously, resulting in a semi-major
axis of , an eccentricity of , and a minimum
mass of the secondary of . Additional short-period RV
variations closely resemble the signal of a Jupiter-mass planet orbiting the
evolved primary component with a period of , but the period and
amplitude of the putative orbit change strongly over time. Furthermore, in our
stability analysis of the system, no stable orbits could be found in a large
region around the best fit. Both of these findings deem a planetary cause of
the RV variations unlikely. Most of the investigated alternative scenarios,
such as an hierarchical triple or stellar spots, also fail to explain the
observed variability convincingly. Due to its very eccentric binary orbit, it
seems possible, however, that Cyg could be an extreme example of a
heartbeat system.Comment: 17 pages, 13 figures, accepted to A&
The global oscillation network group site survey. II. Results
The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable components analysis. An accompanying paper describes the analysis methods in detail; here we present the results of both the network and individual site analyses.
The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 × 10⁻⁴ with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum
The global oscillation network group site survey. II. Results
The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable components analysis. An accompanying paper describes the analysis methods in detail; here we present the results of both the network and individual site analyses.
The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 × 10⁻⁴ with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum
The TESS-Keck Survey. XI. Mass Measurements for Four Transiting sub-Neptunes orbiting K dwarf TOI-1246
Multi-planet systems are valuable arenas for investigating exoplanet architectures and comparing planetary siblings. TOI-1246 is one such system, with a moderately bright K dwarf (V=11.6, K=9.9) and four transiting sub-Neptunes identified by TESS with orbital periods of 4.31 d, 5.90 d, 18.66 d, and 37.92 d. We collected 130 radial velocity observations with Keck/HIRES and TNG/HARPS-N to measure planet masses. We refit the 14 sectors of TESS photometry to refine planet radii (2.97±0.06 R⊕,2.47±0.08 R⊕,3.46±0.09 R⊕, 3.72±0.16 R⊕), and confirm the four planets. We find that TOI-1246 e is substantially more massive than the three inner planets (8.1±1.1M⊕, 8.8±1.2M⊕, 5.3±1.7M⊕, 14.8±2.3M⊕). The two outer planets, TOI-1246 d and TOI-1246 e, lie near to the 2:1 resonance (Pe/Pd=2.03) and exhibit transit timing variations. TOI-1246 is one of the brightest four-planet systems, making it amenable for continued observations. It is one of only six systems with measured masses and radii for all four transiting planets. The planet densities range from 0.70±0.24 to 3.21±0.44g/cm3, implying a range of bulk and atmospheric compositions. We also report a fifth planet candidate found in the RV data with a minimum mass of 25.6 ± 3.6 M⊕. This planet candidate is exterior to TOI-1246 e with a candidate period of 93.8 d, and we discuss the implications if it is confirmed to be planetary in nature