scholarly journals GRASS: Distinguishing Planet-induced Doppler Signatures from Granulation with a Synthetic Spectra Generator

2021 ◽  
Vol 163 (1) ◽  
pp. 11
Author(s):  
Michael L. Palumbo III ◽  
Eric B. Ford ◽  
Jason T. Wright ◽  
Suvrath Mahadevan ◽  
Alexander W. Wise ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Center Of Mass ◽  
Magnetic Activity ◽  
Spectral Variability ◽  
Solar Absorption ◽  
Doppler Shifts ◽  
Solar Observations ◽  
Synthetic Spectra ◽  
Magnetohydrodynamic Simulations ◽  
Observation Strategies

Abstract Owing to recent advances in radial-velocity instrumentation and observation techniques, the detection of Earth-mass planets around Sun-like stars may soon be primarily limited by intrinsic stellar variability. Several processes contribute to this variability, including starspots, pulsations, and granulation. Although many previous studies have focused on techniques to mitigate signals from pulsations and other types of magnetic activity, granulation noise has to date only been partially addressed by empirically motivated observation strategies and magnetohydrodynamic simulations. To address this deficit, we present the GRanulation And Spectrum Simulator (GRASS), a new tool designed to create time-series synthetic spectra with granulation-driven variability from spatially and temporally resolved observations of solar absorption lines. In this work, we present GRASS, detail its methodology, and validate its model against disk-integrated solar observations. As a first-of-its-kind empirical model for spectral variability due to granulation in a star with perfectly known center-of-mass radial-velocity behavior, GRASS is an important tool for testing new methods of disentangling granular line-shape changes from true Doppler shifts.

scholarly journals ‘Sumer’ – Solar Ultraviolet Measurements of Emitted Radiation

1994 ◽  
Vol 144 ◽  
pp. 619-624 ◽  
Author(s):  
K. Wilhelm ◽  
W. Curdt ◽  
A. H. Gabriel ◽  
M. Grewing ◽  
M. C. E. Huber ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Extreme Ultraviolet ◽  
Flow Characteristics ◽  
Magnetic Activity ◽  
High Accuracy ◽  
The Sun ◽  
Lower Corona ◽  
Doppler Shifts ◽  
Solar Magnetic Activity ◽  
Solar Ultraviolet

AbstractThe experiment Solar Ultraviolet Measurements of Emitted Radiation (SUMER) is designed for the investigations of plasma flow characteristics, turbulence and wave motions, plasma densities and temperatures, structures and events associated with solar magnetic activity in the chromosphere, the transition zone and the corona. Specifically, SUMER will measure profiles and intensities of extreme ultraviolet (EUV) lines emitted in the solar atmosphere ranging from the upper chromosphere to the lower corona; determine line broadenings, spectral positions and Doppler shifts with high accuracy; provide stigmatic images of selected areas of the Sun in the EUV with high spatial, temporal and spectral resolution and obtain full images of the Sun and the inner corona in selectable EUV lines, corresponding to a temperature range from 104to more than 1.8 x 106K. The spatial and spectral resolution capabilities of the instrument will be considered in this contribution in some detail, and a new detector concept will be introduced.

scholarly journals Gemini/Phoenix H-band analysis of the globular cluster AL 3

2021 ◽  
Vol 648 ◽  
pp. A16
Author(s):  
B. Barbuy ◽  
H. Ernandes ◽  
S. O. Souza ◽  
R. Razera ◽  
T. Moura ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Wavelength Range ◽  
Globular Cluster ◽  
Spectral Region ◽  
Wavelength Region ◽  
Individual Stars ◽  
Synthetic Spectra ◽  
Cool Stars ◽  
Magnitude Diagram ◽  
The Phoenix

Context. The globular cluster AL 3 is old and located in the inner bulge. Three individual stars were observed with the Phoenix spectrograph at the Gemini South telescope. The wavelength region contains prominent lines of CN, OH, and CO, allowing the derivation of C, N, and O abundances of cool stars. Aims. We aim to derive C, N, O abundances of three stars in the bulge globular cluster AL 3, and additionally in stars of NGC 6558 and HP 1. The spectra of AL 3 allows us to derive the cluster’s radial velocity. Methods. For AL 3, we applied a new code to analyse its colour-magnitude diagram. Synthetic spectra were computed and compared to observed spectra for the three clusters. Results. We present a detailed identification of lines in the spectral region centred at 15 555 Å, covering the wavelength range 15 525–15 590 Å. C, N, and O abundances are tentatively derived for the sample stars.

High Velocity Spectroscopic Binary Orbits from Photoelectric Radial Velocities: BD+20 5152, a Possible Triple System

2010 ◽  
Vol 19 (3-4) ◽  
Author(s):  
J. Sperauskas ◽  
A. Bartkevičius ◽  
R. P. Boyle ◽  
V. Deveikis
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
High Velocity ◽  
Triple System ◽  
Mass Velocity ◽  
Center Of Mass ◽  
Primary Component ◽  
Eccentric Orbit ◽  
Velocity Measurements ◽  
Spectroscopic Binary

AbstractThe spectroscopic orbit of a high proper motion star, BD+20 5152, is calculated from 34 CORAVEL-type radial velocity measurements. The star has a slightly eccentric orbit with a period of 5.70613 d, half-amplitude of 47.7 km/s and eccentricity of 0.049. The center-of-mass velocity of the system is -24.3 km/s. BD+20 5152 seems to be a triple system consisting of a G8 dwarf as a primary component and of two K6-M0 dwarfs as secondary and tertiary components. This model is based on the analysis of its UBVRI and JHK magnitudes. According to the SuperWASP photometry, spots on the surface of the primary are suspected. The excessive brightness in the Galex FUV and NUV magnitudes and a non-zero eccentricity suggest the age of this system to be less than 1 Gyr.

scholarly journals Three years of Sun-as-a-star radial-velocity observations on the approach to solar minimum

2019 ◽  
Vol 487 (1) ◽  
pp. 1082-1100 ◽  
Author(s):  
A Collier Cameron ◽  
A Mortier ◽  
D Phillips ◽  
X Dumusque ◽  
R D Haywood ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Zero Point ◽  
Spatially Resolved ◽  
Solar Observations ◽  
Bayesian Mixture Model ◽  
Mixture Model Approach ◽  
Calibration Uncertainty ◽  
Bayesian Mixture ◽  
Solar Type ◽  
Line Asymmetry

Abstract The time-variable velocity fields of solar-type stars limit the precision of radial-velocity determinations of their planets’ masses, obstructing detection of Earth twins. Since 2015 July, we have been monitoring disc-integrated sunlight in daytime using a purpose-built solar telescope and fibre feed to the HARPS-N stellar radial-velocity spectrometer. We present and analyse the solar radial-velocity measurements and cross-correlation function (CCF) parameters obtained in the first 3 yr of observation, interpreting them in the context of spatially resolved solar observations. We describe a Bayesian mixture-model approach to automated data-quality monitoring. We provide dynamical and daily differential-extinction corrections to place the radial velocities in the heliocentric reference frame, and the CCF shape parameters in the sidereal frame. We achieve a photon-noise-limited radial-velocity precision better than 0.43 m s−1 per 5-min observation. The day-to-day precision is limited by zero-point calibration uncertainty with an RMS scatter of about 0.4 m s−1. We find significant signals from granulation and solar activity. Within a day, granulation noise dominates, with an amplitude of about 0.4 m s−1 and an autocorrelation half-life of 15 min. On longer time-scales, activity dominates. Sunspot groups broaden the CCF as they cross the solar disc. Facular regions temporarily reduce the intrinsic asymmetry of the CCF. The radial-velocity increase that accompanies an active-region passage has a typical amplitude of 5 m s−1 and is correlated with the line asymmetry, but leads it by 3 d. Spectral line-shape variability thus shows promise as a proxy for recovering the true radial velocity.

scholarly journals Stellar activity and coronal heating: an overview of recent results

2015 ◽  
Vol 373 (2042) ◽  
pp. 20140259 ◽  
Author(s):  
Paola Testa ◽  
Steven H. Saar ◽  
Jeremy J. Drake
Keyword(s):  
Magnetic Activity ◽  
Coronal Heating ◽  
Complementary Information ◽  
Stellar Activity ◽  
X Ray ◽  
Solar Observations ◽  
Term Evolution ◽  
Wide Range ◽  
Stellar Magnetic Fields

Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars.

scholarly journals TODCOR: A Two-Dimensional Correlation of a Composite Spectrum to Derive the Radial Velocities of its Components

1992 ◽  
Vol 135 ◽  
pp. 164-166
Author(s):  
Tsevi Mazeh ◽  
Shay Zucker
Keyword(s):  
Radial Velocity ◽  
Cross Correlation ◽  
Radial Velocities ◽  
Two Dimensional ◽  
One Dimensional ◽  
Independent Variables ◽  
Doppler Shifts ◽  
Correlation Algorithm ◽  
Potential Difficulty ◽  
The One

Cross correlation is a frequently used technique to obtain the Doppler shifts of digitized celestial spectra. This method, suggested by Tonry & Davis (1979), cross correlates the observed spectrum against an assumed template, and obtains the stellar radial velocity by the location of the correlation maximum (Wyatt 1985). The technique finds the correct radial velocity even for extremely low S/N spectra.Spectra composed of two components present a potential difficulty to this technique. The cross correlation of these spectra usually displays a double peak which can not be resolved whenever the relative velocity of the two components is small. To overcome this difficulty, we developed TODCOR — a new TwO-Dimensional CORrelation algorithm which can simultaneously derive the Doppler shifts of the two components.TODCOR assumes that the observed spectrum is a combination of two known spectra with unknown shifts. Following the one-dimensional technique, the algorithm calculates the correlation of the observed spectrum against a set of combinations of two templates, with all possible shifts. The correlation, thus, is a two-dimensional function, whose two independent variables are the radial velocities of the two components. The location of the maximum of this function corresponds to the actual Doppler shifts of the two components.

scholarly journals A HARPS RV search for planets around young nearby stars

2020 ◽  
Vol 633 ◽  
pp. A44 ◽  
Author(s):  
A. Grandjean ◽  
A.-M. Lagrange ◽  
M. Keppler ◽  
N. Meunier ◽  
L. Mignon ◽  
...  
Keyword(s):  
Time Series ◽  
Radial Velocity ◽  
Spectroscopic Data ◽  
Imaging Techniques ◽  
Giant Planet ◽  
Magnetic Activity ◽  
Young Stars ◽  
Upper Limits ◽  
Nearby Stars ◽  
Low Mass

Context. Young nearby stars are good candidates in the search for planets with both radial velocity (RV) and direct imaging techniques. This, in turn, allows for the computation of the giant planet occurrence rates at all separations. The RV search around young stars is a challenge as they are generally faster rotators than older stars of similar spectral types and they exhibit signatures of magnetic activity (spots) or pulsation in their RV time series. Specific analyses are necessary to characterize, and possibly correct for, this activity. Aims. Our aim is to search for planets around young nearby stars and to estimate the giant planet (GP) occurrence rates for periods up to 1000 days. Methods. We used the HARPS spectrograph on the 3.6 m telescope at La Silla Observatory to observe 89 A−M young (<600 Myr) stars. We used our SAFIR (Spectroscopic data via Analysis of the Fourier Interspectrum Radial velocities) software to compute the RV and other spectroscopic observables. Then, we computed the companion occurrence rates on this sample. Results. We confirm the binary nature of HD 177171, HD 181321 and HD 186704. We report the detection of a close low mass stellar companion for HIP 36985. No planetary companion was detected. We obtain upper limits on the GP (<13 MJup) and BD (∈ [13;80] MJup) occurrence rates based on 83 young stars for periods less than 1000 days, which are set, 2−2+3 and 1−1+3%.

scholarly journals Absolute Measurements of Starspot Area and Temperature

1993 ◽  
Vol 137 ◽  
pp. 193-195
Author(s):  
James E. Neff ◽  
Douglas O’Neal ◽  
Steven H. Saar
Keyword(s):  
Magnetic Field ◽  
Magnetic Activity ◽  
Local Magnetic Field ◽  
The Sun ◽  
Late Type ◽  
Solar Observations ◽  
Absolute Measure ◽  
Standard Picture ◽  
Stellar Properties ◽  
Absolute Measurements

Photometric and spectroscopic variability of late-type stars frequently has been interpreted as evidence of magnetic activity. The standard picture of stellar activity – inherited from solar observations – includes cool, dark “spots” in the photosphere and hot, dense regions in the chromosphere and coronae. The immediate cause of each of these phenomena is a closed topology of the local magnetic field. Because stars appear as mere points of light, these localized phenomena have not been directly resolvable on stars other than the Sun. Most observed effects are produced by an asymmetric distribution of starspots. If the distribution is symmetric, it would escape detection by most current techniques of light-curve and line-profile modeling. Even more troubling, the stellar properties measured with these techniques describe only a difference between contrasting hemispheres, not an absolute measure.

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