scholarly journals Discovery, TESS Characterization, and Modeling of Pulsations in the Extremely Low-mass White Dwarf GD 278

2021 ◽  
Vol 922 (2) ◽  
pp. 220
Author(s):  
Isaac D. Lopez ◽  
J. J. Hermes ◽  
Leila M. Calcaferro ◽  
Keaton J. Bell ◽  
Adam Samuels ◽  
...  
Keyword(s):  
White Dwarf ◽  
Rotation Rate ◽  
Rotation Period ◽  
Pulsation Period ◽  
Stellar Rotation ◽  
Mode Identification ◽  
Extended Space ◽  
Short Period ◽  
Low Mass ◽  
Best Fit

Abstract We report the discovery of pulsations in the extremely low-mass (ELM), likely helium-core white dwarf GD 278 via ground- and space-based photometry. GD 278 was observed by the Transiting Exoplanet Survey Satellite (TESS) in Sector 18 at a 2 minute cadence for roughly 24 days. The TESS data reveal at least 19 significant periodicities between 2447 and 6729 s, one of which is the longest pulsation period ever detected in a white dwarf. Previous spectroscopy found that this white dwarf is in a 4.61 hr orbit with an unseen >0.4 M ⊙ companion and has T eff = 9230 ± 100 K and log g = 6.627 ± 0.056 , which corresponds to a mass of 0.191 ± 0.013 M ⊙. Patterns in the TESS pulsation frequencies from rotational splittings appear to reveal a stellar rotation period of roughly 10 hr, making GD 278 the first ELM white dwarf with a measured rotation rate. The patterns inform our mode identification for asteroseismic fits, which, unfortunately, do not reveal a global best-fit solution. Asteroseismology reveals two main solutions roughly consistent with the spectroscopic parameters of this ELM white dwarf, but with vastly different hydrogen-layer masses; future seismic fits could be further improved by using the stellar parallax. GD 278 is now the tenth known pulsating ELM white dwarf; it is only the fifth known to be in a short-period binary, but is the first with extended, space-based photometry.

scholarly journals The EBLM project – VII. Spin–orbit alignment for the circumbinary planet host EBLM J0608-59 A/TOI-1338 A

2020 ◽  
Vol 497 (2) ◽  
pp. 1627-1633 ◽  
Author(s):  
Vedad Kunovac Hodžić ◽  
Amaury H M J Triaud ◽  
David V Martin ◽  
Daniel C Fabrycky ◽  
Heather M Cegla ◽  
...  
Keyword(s):  
Rotation Period ◽  
Primary Component ◽  
High Resolution Spectroscopy ◽  
Spin Orbit ◽  
Primary Star ◽  
Secondary Star ◽  
Short Period ◽  
Low Mass ◽  
Detached Binaries ◽  
Binary Orbit

ABSTRACT A dozen short-period detached binaries are known to host transiting circumbinary planets. In all circumbinary systems so far, the planetary and binary orbits are aligned within a couple of degrees. However, the obliquity of the primary star, which is an important tracer of their formation, evolution, and tidal history, has only been measured in one circumbinary system until now. EBLM J0608-59/TOI-1338 is a low-mass eclipsing binary system with a recently discovered circumbinary planet identified by TESS. Here, we perform high-resolution spectroscopy during primary eclipse to measure the projected stellar obliquity of the primary component. The obliquity is low, and thus the primary star is aligned with the binary and planetary orbits with a projected spin–orbit angle β = 2${_{.}^{\circ}}$8 ± 17${_{.}^{\circ}}$1. The rotation period of 18.1 ± 1.6 d implied by our measurement of vsin i⋆ suggests that the primary has not yet pseudo-synchronized with the binary orbit, but is consistent with gyrochronology and weak tidal interaction with the binary companion. Our result, combined with the known coplanarity of the binary and planet orbits, is suggestive of formation from a single disc. Finally, we considered whether the spectrum of the faint secondary star could affect our measurements. We show through simulations that the effect is negligible for our system, but can lead to strong biases in vsin i⋆ and β for higher flux ratios. We encourage future studies in eclipse spectroscopy test the assumption of a dark secondary for flux ratios ≳1 ppt.

scholarly journals HADES RV program with HARPS-N at the TNG

2019 ◽  
Vol 622 ◽  
pp. A193 ◽  
Author(s):  
L. Affer ◽  
M. Damasso ◽  
G. Micela ◽  
E. Poretti ◽  
G. Scandariato ◽  
...  
Keyword(s):  
Rotation Period ◽  
Activity Cycle ◽  
Physical Parameters ◽  
Correlated Noise ◽  
Minimum Mass ◽  
Stellar Rotation ◽  
Orbital Parameters ◽  
Photometric Observations ◽  
Depth Analysis ◽  
Low Mass

Aims. The HArps-n red Dwarf Exoplanet Survey (HADES) is providing a major contribution to the widening of the current statistics of low-mass planets, through the in-depth analysis of precise radial-velocity (RV) measurements in a narrow range of spectral sub-types. Using the HARPS-N spectrograph we reach the precision needed to detect small planets with a few earth masses. Our survey is mainly focused on the M-dwarf population of the northern hemisphere. Methods. As part of that program, we obtained RV measurements of Gl 686, an M1 dwarf at d = 8.2 pc. These measurements show a dispersion much in excess of their internal errors. The analysis of data obtained within an intensive observing campaign demonstrates that the excess dispersion is due to a coherent signal with a period of 15.53 d. Almost simultaneous photometric observations were carried out within the APACHE and EXORAP programs to characterize the stellar activity and to distinguish periodic variations related to activity from signals due to the presence of planetary companions, complemented also with ASAS photometric data. We used a Bayesian framework to estimate the orbital parameters and the planet minimum mass, and to properly treat the activity noise. We took advantage of the available RV measurements for this target from other observing campaigns. The analysis of the RV composite time series from the HIRES, HARPS, and HARPS-N spectrographs, consisting of 198 measurements taken over 20 yr, enabled us to address the nature of periodic signals and also to characterize stellar physical parameters (mass, temperature, and rotation). Results. We report the discovery of a super-Earth orbiting at a distance of 0.092 AU from the host star Gl 686. The planet has a minimum mass of 7.1 ± 0.9 M⊕ and an orbital period of 15.532 ± 0.002 d. The analysis of the activity indexes, of the correlated noise through a Gaussian process framework, and of the photometry provides an estimate of the stellar rotation period at 37 d, and highlights the variability of the spot configuration during the long timespan covering 20 yr. The observed periodicities around 2000 d likely point to the existence of an activity cycle.

scholarly journals Stellar rotation bifurcation caused by tidal locking in the open cluster NGC 2287?

2019 ◽  
Vol 14 (S351) ◽  
pp. 228-232
Author(s):  
Weijia Sun ◽  
Chengyuan Li ◽  
Licai Deng ◽  
Richard de Grijs
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Milky Way ◽  
Open Cluster ◽  
Mass Ratio ◽  
Stellar Rotation ◽  
Rotation Rates ◽  
Short Period ◽  
Low Mass ◽  
Low Mass Ratio

AbstractWe present a detailed analysis of the projected stellar rotational velocities of the well-separated double main sequence (MS) in the young, ∼200 Myr-old Milky Way open cluster NGC 2287 and suggest that stellar rotation may drive the split MSs in NGC 2287. We find that the observed distribution of projected stellar rotation velocities could result from a dichotomous distribution of stellar rotation rates. We discuss whether our observations may reflect the effects of tidal locking affecting a fraction of the cluster’s member stars in stellar binary systems. The slow rotators are likely stars that initially rotated rapidly but subsequently slowed down through tidal locking induced by low-mass-ratio binary systems. However, the cluster may have a much larger population of short-period binaries than is usually seen in the literature, with relatively low secondary masses.

scholarly journals The Interaction of Accretion Flux with Stellar Pulsation

1977 ◽  
Vol 42 ◽  
pp. 340-341
Author(s):  
J.C. Papaloizou ◽  
J.E. Pringle
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Rotation Period ◽  
Low Frequency ◽  
Wave Number ◽  
Slow Rotation ◽  
Short Period ◽  
Effects Of Rotation ◽  
Rotating Star

We consider the usual hypothesis that the short period coherent oscillations seen in cataclysmic variables are attributable to g-modes in a slowly rotating star, for details see Papaloizou and Pringle (1977). We show that this hypothesis is untenable for three main reasons: (i) the observed periods are too short for reasonable white dwarf models, (ii) the observed variability of the oscillations is too rapid and (iii) the expected rotation of the white dwarf, due to accretion, invalidates the slow rotation assumption on which standard g-mode theory is based. We investigate the low frequency spectrum of a rotating pulsating star, taking the effects of rotation fully into account. In this case there are two sets of low frequency modes, the g-modes, and modes similar to Rossby waves in the Earth’s atmosphere and oceans, which we designate r-modes. Typical periods for such modes are 1/m times the rotation period of the white dwarfs outer layers (m is the azimuthal wave number). We conclude that non-radial oscillations of white dwarfs can account for the properties of the oscillations seen in dwarf novae.

scholarly journals HADES RV Programme with HARPS-N at TNG

2019 ◽  
Vol 624 ◽  
pp. A27 ◽  
Author(s):  
E. González-Álvarez ◽  
G. Micela ◽  
J. Maldonado ◽  
L. Affer ◽  
A. Maggio ◽  
...  
Keyword(s):  
Rotation Period ◽  
High Resolution Spectroscopy ◽  
Slow Rotation ◽  
Stellar Rotation ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Rotation Periods ◽  
Coronal Activity ◽  
Low Mass ◽  
M Dwarf Stars

Aims. We extend the relationship between X-ray luminosity (Lx) and rotation period (Prot) found for main-sequence FGK stars, and test whether it also holds for early M dwarfs, especially in the non-saturated regime (Lx ∝ Prot−2) which corresponds to slow rotators. Methods. We use the luminosity coronal activity indicator (Lx) of a sample of 78 early M dwarfs with masses in the range from 0.3 to 0.75 M⊙ from the HArps-N red Dwarf Exoplanet Survey (HADES) radial velocity (RV) programme collected from ROSAT and XMM-Newton. The determination of the rotation periods (Prot) was done by analysing time series of high-resolution spectroscopy of the Ca II H & K and Hα activity indicators. Our sample principally covers the slow rotation regime with rotation periods from 15 to 60 days. Results. Our work extends to the low mass regime the observed trend for more massive stars showing a continuous shift of the Lx∕Lbol versus Prot power law towards longer rotation period values, and includes a more accurate way to determine the value of the rotation period at which the saturation occurs (Psat) for M dwarf stars. Conclusions. We conclude that the relations between coronal activity and stellar rotation for FGK stars also hold for early M dwarfs in the non-saturated regime, indicating that the rotation period is sufficient to determine the ratio Lx∕Lbol.

scholarly journals Disentangling between stellar activity and planetary signals

2010 ◽  
Vol 6 (S273) ◽  
pp. 281-285 ◽  
Author(s):  
Isabelle Boisse ◽  
François Bouchy ◽  
Guillaume Hébrard ◽  
Xavier Bonfils ◽  
Nuno Santos ◽  
...  
Keyword(s):  
Orbital Period ◽  
Rotational Period ◽  
Stellar Rotation ◽  
Stellar Activity ◽  
Short Period ◽  
Stellar Photosphere ◽  
Low Mass ◽  
Host Stars

AbstractPhotospheric stellar activity (i.e. dark spots or bright plages) might be an important source of noise and confusion in the radial-velocity (RV) measurements. Radial-velocimetry planet search surveys as well as follow-up of photometric transit surveys require a deeper understanding and characterization of the effects of stellar activities to disentangle it from planetary signals.We simulate dark spots on a rotating stellar photosphere. The variations of the RV are characterized and analyzed according to the stellar inclination, the latitude and the number of spots. The Lomb-Scargle periodograms of the RV variations induced by activity present power at the rotational period Prot of the star and its two-first harmonics Prot/2 and Prot/3. Three adjusted sinusoids fixed at the fundamental period and its two-first harmonics allow to remove about 90% of the RV jitter amplitude. We apply and validate our approach on four known active planet-host stars: HD 189733, GJ 674, CoRoT-7 and ι Hor. We succeed in fitting simultaneously activity and planetary signals on GJ674 and CoRoT-7. We excluded short-period low-mass exoplanets around ι Hor. Our approach is efficient to disentangle reflex-motion due to a planetary companion and stellar-activity induced-RV variations provided that 1) the planetary orbital period is not close to that of the stellar rotation or one of its two-first harmonics, 2) the rotational period of the star is accurately known, 3) the data cover more than one stellar rotational period.

scholarly journals The HADES RV programme with HARPS-N at TNG

2019 ◽  
Vol 625 ◽  
pp. A126 ◽  
Author(s):  
M. Pinamonti ◽  
A. Sozzetti ◽  
P. Giacobbe ◽  
M. Damasso ◽  
G. Scandariato ◽  
...  
Keyword(s):  
Time Series ◽  
Activity Index ◽  
Rotation Period ◽  
Gaussian Process Regression ◽  
Formation Mechanisms ◽  
Stellar Rotation ◽  
Dwarf Planets ◽  
Depth Analysis ◽  
Low Mass ◽  
Photometric Measurements

Context. Small rocky planets seem to be very abundant around low-mass M-type stars. Their actual planetary population is however not yet precisely understood. Currently, several surveys aim to expand the statistics with intensive detection campaigns, both photometric and spectroscopic. Aims. The HADES program aims to improve the current statistics through the in-depth analysis of accurate radial-velocity (RV) monitoring in a narrow range of spectral sub-types, with the precision needed to detect small planets with a few Earth masses. Methods. We analyse 106 spectroscopic HARPS-N observations of the active M0-type star GJ 685 taken over the past five years. We combine these data with photometric measurements from different observatories to accurately model the stellar rotation and disentangle its signals from genuine Doppler planetary signals in the RV data. We run an MCMC analysis on the RV and activity index time series to model the planetary and stellar signals present in the data, applying Gaussian Process regression technique to deal with the stellar activity signals. Results. We identify three periodic signals in the RV time series, with periods of 9, 24, and 18 d. Combining the analyses of the photometry of the star with the activity indexes derived from the HARPS-N spectra, we identify the 18 d and 9 d signals as activity-related, corresponding to the stellar rotation period and its first harmonic, respectively. The 24 d signal shows no relation to any activity proxy, and therefore we identify it as a genuine planetary signal. We find the best-fit model describing the Doppler signal of the newly found planet, GJ 685 b, corresponding to an orbital period Pb = 24.160−0.047+0.061 d and a minimum mass MP sin i = 9.0−1.8+1.7 M⊕. We also study a sample of 70 RV-detected M-dwarf planets, and present new statistical evidence of a difference in mass distribution between the populations of single- and multi-planet systems, which can shed new light on the formation mechanisms of low-mass planets around late-type stars.

A Spectroscopic and Photometric Study of 1H0542-407: A New Magnetic Variable

1987 ◽  
Vol 7 (2) ◽  
pp. 151-158
Author(s):  
D. A. H. Buckley ◽  
I. R. Tuohy
Keyword(s):  
Magnetic Field ◽  
White Dwarf ◽  
Rotation Period ◽  
Mass Function ◽  
X Rays ◽  
Orbital Inclination ◽  
Medium Resolution ◽  
Photometric Observations ◽  
Short Period ◽  
Velocity Variations

AbstractWe report spectroscopic and photometric observations of the new DQ Hercuis system 1H0542-407, recently discovered by us to be the optical counterpart of a HEAO-1 X-ray source. Medium resolution spectroscopy using the AAT in the region λ3930 to λ4960 conducted over consecutive nights shows radial velocity variations at periods of ∼ 1910 s, consistent with the white dwarf rotation period, and 5.7 h, in agreement with the orbital period derived from our EXOSAT observations. The K semi-amplitude velocities are ∼ 50 and 20 km s-1 respectively, leading to a mass function f(M) = 3.3 ± 0.6 × 10-3M⊙ and an orbital inclination close to 20°. The emission line profiles are characterized by simple Gaussians whose FWHM vary at the rotation period. A time series analysis of high resolution photometry conducted on the ANU 2.3 metre telescope reveals the presence of several periodicities, including the orbital sidebands. The dominant sideband (Vr − Vo) arises from X-rays reprocessed in a region corotating at the orbital frequency. A model is developed for 1H0542-407 which indicates that the accretion disk is disrupted at ∼5Rwd by the primary’s magnetic field. The short period velocity variations arise within the magnetosphere. A white dwarf magnetic field strength of < ∼ 3 MG is implied.

scholarly journals The influence of planetary engulfment on stellar rotation in metal-poor main-sequence stars

2020 ◽  
Vol 643 ◽  
pp. A34
Author(s):  
A. Oetjens ◽  
L. Carone ◽  
M. Bergemann ◽  
A. Serenelli
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Rotation Velocity ◽  
Occurrence Rate ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Semi Major Axis ◽  
Dynamical Interaction ◽  
Tidal Interaction ◽  
Low Mass

Context. The method of gyrochronology relates the age of its star to its rotation period. However, recent evidence of deviations from gyrochronology relations has been reported in the literature. Aims. We study the influence of tidal interaction between a star and its companion on the rotation velocity of the star to explain peculiar stellar rotation velocities. Methods. We followed the interaction of a star and its planet using a comprehensive numerical framework that combines tidal friction, magnetic braking, planet migration, and detailed stellar evolution models from the GARSTEC grid. We focus on close-in companions from 1 to 20 MJup orbiting low-mass (0.8 − 1 M⊙) main-sequence stars with a broad metallicity of [Fe/H] = − 1 up to solar. Results. Our simulations suggest that the dynamical interaction between a star and its companion can have different outcomes that depend on the initial semi-major axis and the mass of the planet, as well as on the mass and metallicity of its host star. In most cases, especially in the case of planet engulfment, we find a catastrophic increase in stellar rotation velocity from 1 kms−1 to over 40 kms−1 while the star is still on the main-sequence. The main prediction of our model is that low-mass main-sequence stars with abnormal rotation velocities should be more common at low-metallicity, as lower [Fe/H] favours faster planet engulfment, based on the assumption that the occurrence rate of close-in massive planets is similar at all metallicities. Conclusions. Our scenario explains peculiar rotation velocities of low-mass main-sequence stars by the tidal interaction between the star and its companion. Current observational samples are too narrow and incomplete, and, thus, they are not sufficient for our model to be tested.

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