scholarly journals The accelerating rotation of the magnetic He-weak star HD 142990

2019 ◽  
Vol 486 (4) ◽  
pp. 5558-5566 ◽  
Author(s):  
M Shultz ◽  
Th Rivinius ◽  
B Das ◽  
G A Wade ◽  
P Chandra
Keyword(s):  
Rotation Period ◽  
Photometric Data ◽  
Data Sets ◽  
Surface Magnetic Field ◽  
Short Rotation ◽  
Magnetic Stars ◽  
Weak Star ◽  
Rotational Evolution ◽  
Strong Surface ◽  
Rapid Rotator

ABSTRACT HD 142990 (V 913 Sco; B5 V) is a He-weak star with a strong surface magnetic field and a short rotation period (Prot ∼ 1 d). Whilst it is clearly a rapid rotator, recent determinations of Prot are in formal disagreement. In this paper, we collect magnetic and photometric data with a combined 40-yr baseline in order to re-evaluate Prot and examine its stability. Both period analysis of individual data sets and O − C analysis of the photometric data demonstrate that Prot has decreased over the past 30 yr, violating expectations from magnetospheric braking models, but consistent with behaviour reported for 2 other hot, rapidly rotating magnetic stars, CU Vir and HD 37776. The available magnetic and photometric time series for HD 142990 can be coherently phased assuming a spin-up rate $\dot{P}$ of approximately −0.6 s yr−1, although there is some indication that $\dot{P}$ may have slowed in recent years, possibly indicating an irregular or cyclic rotational evolution.

scholarly journals Surface Inhomogeneities on the W UMa star AC Bootis

1991 ◽  
Vol 130 ◽  
pp. 376-377
Author(s):  
Albert P. Linnell
Keyword(s):  
Photometric Data ◽  
Model Parameters ◽  
Data Sets ◽  
Roche Model

AbstractNew photometric data and two older data sets for AC Boo can be represented with a common set of Roche model parameters and two starspot pairs which drift only in longitude and are located on the cooler component.

scholarly journals Magnetic fields of intermediate-mass T Tauri stars

2019 ◽  
Vol 622 ◽  
pp. A72 ◽  
Author(s):  
F. Villebrun ◽  
E. Alecian ◽  
G. Hussain ◽  
J. Bouvier ◽  
C. P. Folsom ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Large Population ◽  
T Tauri Stars ◽  
Magnetic Characteristics ◽  
Intermediate Mass ◽  
Surface Magnetic Field ◽  
T Tauri ◽  
Magnetic Stars ◽  
Pms Stars

Context. The origin of the fossil magnetic fields detected in 5 to 10% of intermediate-mass main sequence stars is still highly debated.Aims. We want to bring observational constraints to a large population of intermediate-mass pre-main sequence (PMS) stars in order to test the theory that convective-dynamo fields generated during the PMS phases of stellar evolution can occasionally relax into fossil fields on the main sequence.Methods. Using distance estimations, photometric measurements, and spectropolarimetric data from HARPSpol and ESPaDOnS of 38 intermediate-mass PMS stars, we determined fundamental stellar parameters (Teff,Landvsini) and measured surface magnetic field characteristics (including detection limits for non-detections, and longitudinal fields and basic topologies for positive detections). Using PMS evolutionary models, we determined the mass, radius, and internal structure of these stars. We compared different PMS models to check that our determinations were not model-dependant. We then compared the magnetic characteristics of our sample accounting for their stellar parameters and internal structures.Results. We detect magnetic fields in about half of our sample. About 90% of the magnetic stars have outer convective envelopes larger than ∼25% of the stellar radii, and heavier than ∼2% of the stellar mass. Going to higher mass, we find that the magnetic incidence in intermediate-mass stars drops very quickly, within a timescale on the order of few times 0.1 Myr. Finally, we propose that intermediate-mass T Tauri stars with large convective envelopes, close to the fully convective limit, have complex fields and that their dipole component strengths may decrease as the sizes of their convective envelopes decrease, similar to lower-mass T Tauri stars.

scholarly journals Asteroid (16) Psyche’s primordial shape: A possible Jacobi ellipsoid

2020 ◽  
Vol 638 ◽  
pp. L15 ◽  
Author(s):  
M. Ferrais ◽  
P. Vernazza ◽  
L. Jorda ◽  
N. Rambaux ◽  
J. Hanuš ◽  
...  
Keyword(s):  
Bulk Composition ◽  
Three Dimensional ◽  
Rotation Period ◽  
Data Sets ◽  
Similar Data ◽  
Small Deviations ◽  
3D Shape ◽  
Large Program ◽  
Solar System Object ◽  
Equilibrium Figures

Context. Asteroid (16) Psyche is the largest M-type asteroid in the main belt and the target of the NASA Psyche mission. It is also the only asteroid of this size (D >  200 km) known to be metal rich. Although various hypotheses have been proposed to explain the rather unique physical properties of this asteroid, a perfect understanding of its formation and bulk composition is still missing. Aims. We aim to refine the shape and bulk density of (16) Psyche and to perform a thorough analysis of its shape to better constrain possible formation scenarios and the structure of its interior. Methods. We obtained disk-resolved VLT/SPHERE/ZIMPOL images acquired within our ESO large program (ID 199.C-0074), which complement similar data obtained in 2018. Both data sets offer a complete coverage of Psyche’s surface. These images were used to reconstruct the three-dimensional (3D) shape of Psyche with two independent shape modeling algorithms (MPCD and ADAM). A shape analysis was subsequently performed, including a comparison with equilibrium figures and the identification of mass deficit regions. Results. Our 3D shape along with existing mass estimates imply a density of 4.20  ±  0.60 g cm−3, which is so far the highest for a solar system object following the four telluric planets. Furthermore, the shape of Psyche presents small deviations from an ellipsoid, that is, prominently three large depressions along its equator. The flatness and density of Psyche are compatible with a formation at hydrostatic equilibrium as a Jacobi ellipsoid with a shorter rotation period of ∼3h. Later impacts may have slowed down Psyche’s rotation, which is currently ∼4.2 h, while also creating the imaged depressions. Conclusions. Our results open the possibility that Psyche acquired its primordial shape either after a giant impact while its interior was already frozen or while its interior was still molten owing to the decay of the short-lived radionuclide 26Al.

scholarly journals The magnetic early B-type stars I: magnetometry and rotation

2018 ◽  
Vol 475 (4) ◽  
pp. 5144-5178 ◽  
Author(s):  
M E Shultz ◽  
G A Wade ◽  
Th Rivinius ◽  
C Neiner ◽  
E Alecian ◽  
...  
Keyword(s):  
Magnetic Measurements ◽  
Field Measurements ◽  
Magnetic Interactions ◽  
High Resolution Spectroscopy ◽  
High Dispersion ◽  
Single Element ◽  
Data Sets ◽  
Peculiar Stars ◽  
Magnetic Stars ◽  
Chemically Peculiar Stars

Abstract The rotational and magnetic properties of many magnetic hot stars are poorly characterized, therefore the Magnetism in Massive Stars and Binarity and Magnetic Interactions in various classes of Stars collaborations have collected extensive high-dispersion spectropolarimetric data sets of these targets. We present longitudinal magnetic field measurements 〈Bz〉 for 52 early B-type stars (B5–B0), with which we attempt to determine their rotational periods Prot. Supplemented with high-resolution spectroscopy, low-resolution Dominion Astrophysical Observatory circular spectropolarimetry, and archival Hipparcos photometry, we determined Prot for 10 stars, leaving only five stars for which Prot could not be determined. Rotational ephemerides for 14 stars were refined via comparison of new to historical magnetic measurements. The distribution of Prot is very similar to that observed for the cooler Ap/Bp stars. We also measured v sin i and vmac for all stars. Comparison to non-magnetic stars shows that v sin i is much lower for magnetic stars, an expected consequence of magnetic braking. We also find evidence that vmac is lower for magnetic stars. Least-squares deconvolution profiles extracted using single-element masks revealed widespread, systematic discrepancies in 〈Bz〉 between different elements: this effect is apparent only for chemically peculiar stars, suggesting it is a consequence of chemical spots. Sinusoidal fits to H line 〈Bz〉 measurements (which should be minimally affected by chemical spots), yielded evidence of surface magnetic fields more complex than simple dipoles in six stars for which this has not previously been reported; however, in all six cases, the second- and third-order amplitudes are small relative to the first-order (dipolar) amplitudes.

scholarly journals Determination of the rotational period of the comet 29P/Schwassmann-Wachmann-1 using dynamics of the dust structures (jets) in the coma

2012 ◽  
Vol 10 (H16) ◽  
pp. 176-176
Author(s):  
Aleksandra Ivanova ◽  
Viktor Afanasiev ◽  
Pavlo Korsun ◽  
Aleksandr Baransky ◽  
Maksim Andreev ◽  
...  
Keyword(s):  
Digital Filters ◽  
Cross Correlation ◽  
Rotation Period ◽  
Correlation Method ◽  
Photometric Data ◽  
Rotational Period ◽  
Water Ice ◽  
Ice Sublimation ◽  
Made In

AbstractWe present analysis of the photometric data of the distant comet 29P/Schwassmann-Wachmann-1, obtained at the 6-m BTA telescope (SAO RAS, Russia) and at the 2-meter telescope Zeiss-2000 (ICAMER, KB). The comet shows significant jets activity at large heliocentric distances, beyond the zone of water ice sublimation. Various digital filters were applied to increase the contrast of the jets and separate them. The rotation period of the nucleus was derived using cross-correlation method. The value of the rotation period is 12.1 ± 1.2 days for observations made in 2008 and 11.7 ± 1.5 days for observations made in 2009.

scholarly journals IMPROVED VARIABLE STAR SEARCH IN LARGE PHOTOMETRIC DATA SETS: NEW VARIABLES INCoRoTFIELD LRa02 DETECTED BY BEST II

2012 ◽  
Vol 143 (6) ◽  
pp. 140 ◽  
Author(s):  
T. Fruth ◽  
P. Kabath ◽  
J. Cabrera ◽  
R. Chini ◽  
Sz. Csizmadia ◽  
...  
Keyword(s):  
Variable Star ◽  
Photometric Data ◽  
Data Sets ◽  
New Variables

scholarly journals Time-Series Spectroscopy of ζ Ophiuchi

1993 ◽  
Vol 139 ◽  
pp. 190-190
Author(s):  
A.H.N. Reid ◽  
C.T. Bolton ◽  
R.A. Crowe ◽  
M.S. Fieldus ◽  
A.W. Fullerton ◽  
...  
Keyword(s):  
Time Series ◽  
Rotation Period ◽  
Phase Changes ◽  
High Signal ◽  
Line Profiles ◽  
Rotational Modulation ◽  
Multi Wavelength ◽  
Rapid Rotator ◽  
Multi Mode ◽  
Radial Pulsations

AbstractWe have undertaken a multi-site, multi-wavelength observing campaign on the archetypal O stars ζ Puppis (O4 I(n)f) and ζ Ophiuchi (O9.5 V). Both stars are well known for the strength of their line profile variations (lpv's), and represent extremes of O spectral type and luminosity class. UV time-series spectroscopy of ζ Pup and ζ Oph is described by Prinja et al. (Ap.J. 1992, 390, 266), and Howarth et al. (Ap.J. 1992, submitted) respectively. The optical spectroscopic results of ζ Oph are reported by Reid et al. (1992, ApJ submitted), of which some of the principal results are given here.During late April, and early May, 1989, we obtained high-resolution, high signal-to-noise optical spectra of the late O-type, rapid rotator ζ Oph. Time-series analysis, using the CLEAN algorithm, has shown that the characteristic lpv seen in HeI λ447lÅ, Si III λλ4552, 4567, 4575Å, and MgII λ448lÅ can be satisfactorily represented as a set of 4 sinusoids. No substantial variation is observed in HeII λ4541, or NIII λ4517Å. We attribute this behaviour to a combination of equatorial gravity-darkening and a latitudinally-confined origin for the lpv.The phase changes over the line profiles indicate repetitive patterns of axial symmetry, rotating prograde in the co-rotating frame of the star. The periods are 3.339 hours (-m = 4), 2.435 hours (-m = 5 or -m = 6), 1.859 hours (-m = 9 ± 1), and either 1.366 hours or 1.292 hours (-m = 11 ± 1); -m represents the spatial frequency around the stellar equator. The first three periods confirm those found at earlier epochs, and we conclude that some lpv characteristics are reproduced over at least a 2-year interval.Since no commensurate superperiod (|m|P) exists, and since the super-periods are less than our estimated minimum rotation period for ζ Oph (> 18 hours), we reject a rotational modulation origin for the lpv and conclude that the star is undergoing multi-mode, sectorial, non-radial pulsations.

scholarly journals Star-planet tidal interaction and the limits of gyrochronology

2019 ◽  
Vol 626 ◽  
pp. A120
Author(s):  
F. Gallet ◽  
P. Delorme
Keyword(s):  
Angular Momentum ◽  
Rotation Rate ◽  
Age Determination ◽  
Rotation Period ◽  
Orbital Evolution ◽  
Tidal Interaction ◽  
Surface Rotation ◽  
Rotational Evolution ◽  
Forbidden Region ◽  
The Impact

Context. Age estimation techniques such as gyrochronology and magnetochronology cannot be applied to stars that have exchanged angular momentum with their close environments. This is especially true for a massive close-in planetary companion (with a period of a few days or less) that could have been strongly impacted by the rotational evolution of the host star, throughout the stellar evolution, through the star-planet tidal interaction. Aims. In this article, we provide the community with a reliable region in which empirical techniques such as gyrochronology can be used with confidence. Methods. We combined a stellar angular momentum evolution code with a planetary orbital evolution code to study in detail the impact of star-planet tidal interaction on the evolution of the surface rotation rate of the star. Results. We show that the interaction of a close-in massive planet with its host star can strongly modify the surface rotation rate of this latter, in most of the cases associated with a planetary engulfment. A modification of the surface rotation period of more than 90% can survive a few hundred Myr after the event and a modification of 10% can last for a few Gyr. In such cases, a gyrochronology analysis of the star would incorrectly make it appear as rejuvenated, thus preventing us from using this method with confidence. To try overcome this issue, we proposed the proof of concept of a new age determination technique that we call the tidal-chronology method, which is based on the observed pair Prot, ⋆–Porb of a given star-planet system, where Prot, ⋆ is the stellar surface rotational period and Porb the planetary orbital period. Conclusions. The gyrochronology technique can only be applied to isolated stars or star-planet systems outside a specific range of Prot, ⋆–Porb. This region tends to expand for increasing stellar and planetary mass. In that forbidden region, or if any planetary engulfment is suspected, gyrochronology should be used with extreme caution, while tidal-chronology could be considered. This technique does not provide a precise age for the system yet; however, it is already an extension of gyrochronology and could be helpful to determine a more precise range of possible ages for planetary systems composed of a star between 0.3 and 1.2 M⊙ and a planet more massive than 1 Mjup initially located at a few hundredths of au from the host star.

scholarly journals Stellar activity analysis of Barnard’s Star: Very slow rotation and evidence for long-term activity cycle

2019 ◽  
Author(s):  
B Toledo-Padrón ◽  
J I González Hernández ◽  
C Rodríguez-López ◽  
A Suárez Mascareño ◽  
R Rebolo ◽  
...  
Keyword(s):  
Time Series ◽  
Spectroscopic Data ◽  
Rotation Period ◽  
Photometric Data ◽  
Activity Level ◽  
Slow Rotation ◽  
Activity Levels ◽  
Stellar Activity

Abstract The search for Earth-like planets around late-type stars using ultra-stable spectrographs requires a very precise characterization of the stellar activity and the magnetic cycle of the star, since these phenomena induce radial velocity (RV) signals that can be misinterpreted as planetary signals. Among the nearby stars, we have selected Barnard’s Star (Gl 699) to carry out a characterization of these phenomena using a set of spectroscopic data that covers about 14.5 years and comes from seven different spectrographs: HARPS, HARPS-N, CARMENES, HIRES, UVES, APF, and PFS; and a set of photometric data that covers about 15.1 years and comes from four different photometric sources: ASAS, FCAPT-RCT, AAVSO, and SNO. We have measured different chromospheric activity indicators (Hα, Ca II HK and Na I D), as well as the FWHM of the cross-correlation function computed for a sub-set of the spectroscopic data. The analysis of Generalized Lomb-Scargle periodograms of the time series of different activity indicators reveals that the rotation period of the star is 145 ± 15 days, consistent with the expected rotation period according to the low activity level of the star and previous claims. The upper limit of the predicted activity-induced RV signal corresponding to this rotation period is about 1 m/s. We also find evidence of a long-term cycle of 10 ± 2 years that is consistent with previous estimates of magnetic cycles from photometric time series in other M stars of similar activity levels. The available photometric data of the star also support the detection of both the long-term and the rotation signals.

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