scholarly journals On the Ultraviolet Photometric Variability of the Helium-Weak B Stars (From ANS Data)

1986 ◽  
Vol 90 ◽  
pp. 271-274
Author(s):  
E.I. Želwanowa ◽  
W. Sohöneich
Keyword(s):  
Open Cluster ◽  
Ultraviolet Region ◽  
Rotational Period ◽  
Slight Improvement ◽  
Photometric Variability ◽  
B Stars ◽  
Photometric Observations

AbstractPhotometric observations in the ultraviolet region obtained by the ANS satellite enabled us: to confirm with a slight improvement the rotational period of HD 22470 (UV lightcurves of HD 22470 compared with u and magnetic curves are shown in fig. 1); to confirm the variability with very small amplitudes for HD 74196, a member of the open cluster IC 2391 (Fig. 2)to compare the amplitude-wavelength relations of some other He-weak stars with known periods (HD 35298, HD 142884, HD 144334, HD 175362, and HD 109026). A preliminary rotational period for the star HD 109026 using the 11 ANS observations was found to be about 1.5 days.

scholarly journals Long-Term Multicolour Photometry of the Young Stellar Objects FHO 26, FHO 27, FHO 28, FHO 29, and V1929 Cygni

2015 ◽  
Vol 32 ◽  
Author(s):  
S. I. Ibryamov ◽  
E. H. Semkov ◽  
S. P. Peneva
Keyword(s):  
Gulf Of Mexico ◽  
Young Stellar Objects ◽  
Main Sequence Stars ◽  
Stellar Objects ◽  
Photometric Variability ◽  
The North ◽  
Dense Molecular Cloud ◽  
Photometric Observations ◽  
All Optical

AbstractResults from long-term multicolour optical photometric observations of the pre-main-sequence stars FHO 26, FHO 27, FHO 28, FHO 29, and V1929 Cyg collected during the period from 1997 June to 2014 December are presented. The objects are located in the dense molecular cloud L935, named ‘Gulf of Mexico’, in the field between the North America and Pelican nebulae. All stars from our study exhibit strong photometric variability in all optical passbands. Using our BVRI observations and data published by other authors, we tried to define the reasons for the observed brightness variations. The presented paper is a part of our long-term photometric study of the young stellar objects in the region of ‘Gulf of Mexico’.

scholarly journals Improved model of the triple system V746 Cassiopeiae that has a bipolar magnetic field associated with the tertiary

2017 ◽  
Vol 609 ◽  
pp. A5
Author(s):  
P. Harmanec ◽  
M. Brož ◽  
P. Mayer ◽  
P. Zasche ◽  
L. Kotková ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Triple System ◽  
Detection Threshold ◽  
Variable Magnetic Field ◽  
Close Binary ◽  
Rotational Period ◽  
Orbital Inclination ◽  
Photometric Observations ◽  
Optical Region ◽  
Improved Model

V746 Cas is known to be a triple system composed of a close binary with an alternatively reported period of either 25\hbox{$.\!\!^{\rm d}$}4 or 27\hbox{$.\!\!^{\rm d}$}8 and a distant third component in a 170 yr (62 000 d) orbit. The object was also reported to exhibit multiperiodic light variations with periods from 0\hbox{$.\!\!^{\rm d}$}83 to 2\hbox{$.\!\!^{\rm d}$}50, on the basis of which it was classified as a slowly pulsating B star. Interest in further investigation of this system was raised by the recent detection of a variable magnetic field. Analysing spectra from four instruments, earlier published radial velocities, and several sets of photometric observations, we arrived at the following conclusions: (1) The optical spectrum is dominated by the lines of the B-type primary (Teff 1 ~ 16 500(100) K), contributing 70% of the light in the optical region, and a slightly cooler B tertiary (Teff 3 ~ 13 620(150) K). The lines of the low-mass secondary are below our detection threshold; we estimate that it could be a normal A or F star. (2) We resolved the ambiguity in the value of the inner binary period and arrived at a linear ephemeris of \hbox{$T_{\rm super.\,conj.}={\rm HJD}~2\,443\,838.78(81)+25\fd41569(42)\times E$}. (3) The intensity of the magnetic field undergoes a sinusoidal variation in phase with one of the known photometric periods, namely 2\hbox{$.\!\!^{\rm d}$}503867(19), which we identify with the rotational period of the tertiary. (4) The second dominant photometric 1\hbox{$.\!\!^{\rm d}$}0649524(40) period is tentatively identified with the rotational period of the broad-lined B-type primary, but this interpretation is much less certain and needs further verification. (5) If our interpretation of photometric periods is confirmed, the classification of the object as a slowly pulsating B star should be revised. (6) Applying an N-body model to different types of available observational data, we can constrain the orbital inclination of the inner orbit to ~60°<i1< 85° even in the absence of binary eclipses, and we estimate the probable properties of the triple system and its components.

scholarly journals Photometric, kinematic, and variability study in the young open cluster NGC 1960

2020 ◽  
Vol 492 (3) ◽  
pp. 3602-3621 ◽  
Author(s):  
Y C Joshi ◽  
J Maurya ◽  
A A John ◽  
A Panchal ◽  
S Joshi ◽  
...  
Keyword(s):  
Open Cluster ◽  
Mass Range ◽  
Mass Function ◽  
Variable Stars ◽  
B Stars ◽  
V Band ◽  
Short Period ◽  
Young Open Cluster ◽  
Mass Segregation ◽  
Variability Study

ABSTRACT We present a comprehensive photometric analysis of a young open cluster NGC 1960 (= M36) along with the long-term variability study of this cluster. Based on the kinematic data of Gaia DR2, the membership probabilities of 3871 stars are ascertained in the cluster field among which 262 stars are found to be cluster members. Considering the kinematic and trigonometric measurements of the cluster members, we estimate a mean cluster parallax of 0.86 ± 0.05 mas and mean proper motions of μRA = −0.143 ± 0.008 mas yr−1 and μDec. = −3.395 ± 0.008 mas yr−1. We obtain basic parameters of the cluster such as E(B − V) = 0.24 ± 0.02 mag, log(Age/yr) = 7.44 ± 0.02, and d = 1.17 ± 0.06 kpc. The mass function slope in the cluster for the stars in the mass range of 0.72–7.32 M⊙ is found to be γ = −1.26 ± 0.19. We find that mass segregation is still taking place in the cluster which is yet to be dynamically relaxed. This work also presents first high-precision variability survey in the central 13 arcmin × 13 arcmin region of the cluster. The V-band photometric data accumulated on 43 nights over a period of more than 3 yr reveals 76 variable stars among which 72 are periodic variables. Among them, 59 are short period (P &lt; 1 d) and 13 are long period (P &gt; 1 d). The variable stars have V magnitudes ranging between 9.1 to 19.4 mag and periods between 41 min and 10.74 d. On the basis of their locations in the H–R diagram, periods, and characteristic light curves, 20 periodic variables belong to the cluster are classified as 2 δ-Scuti, 3 γ-Dor, 2 slowly pulsating B stars, 5 rotational variables, 2 non-pulsating B stars, and 6 as miscellaneous variables.

scholarly journals Activity of (6478) Gault during 2019 January 13–March 28

2020 ◽  
Vol 496 (3) ◽  
pp. 2636-2647
Author(s):  
Oleksandra Ivanova ◽  
Yuri Skorov ◽  
Igor Luk'yanyk ◽  
Dušan Tomko ◽  
Marek Husárik ◽  
...  
Keyword(s):  
Light Curve ◽  
Broad Band ◽  
The Body ◽  
Rotational Period ◽  
Photometric Observations

ABSTRACT We present the results of photometric observations of active asteroid (6478) Gault performed at heliocentric distances from 2.46 to 2.30 au and geocentric distances from 1.79 to 1.42 au between 2019 January 15 and March 28. Observations were carried out at the 2.5-m telescope of SAI MSU (Caucasian Mountain Observatory) on 2019 January 15 and at the 1.3 and 0.61-m telescopes (SPb) on 2019 February 6 and March 28, respectively. The direct images of the asteroid were obtained with the broad-band B, V, and R filters. Comet-like structures were detected at all observation dates. Colour maps were built and colour variations along the tail for the observation made on 2019 January 15 were analysed. The Afρ was calculated for the R filter, and the evaluated value varies from 47 to 32 cm for the period from 2019 January to the end of March. The rotational period of the body is estimated from the light curve by different methods and is about 1.79 h. Possible mechanisms of triggering Gault's activity are discussed.

scholarly journals The Unusual Photometric Variability of the PMS Star GM Cep

2015 ◽  
Vol 32 ◽  
Author(s):  
E. H. Semkov ◽  
S. I. Ibryamov ◽  
S. P. Peneva ◽  
T. R. Milanov ◽  
K. A. Stoyanov ◽  
...  
Keyword(s):  
Open Cluster ◽  
High Amplitude ◽  
Outer Radius ◽  
T Tauri Stars ◽  
Photometric Data ◽  
Spectral Studies ◽  
Photometric Variability ◽  
T Tauri ◽  
Young Open Cluster ◽  
Photometric Monitoring

AbstractResults from UBVRI photometric observations of the pre-main sequence star GM Cep obtained in the period 2011 April–2014 August are reported in the paper. Presented data are a continuation of our photometric monitoring of the star started in 2008. GM Cep is located in the field of the young open cluster Trumpler 37 and over the past years it has been an object of intense photometric and spectral studies. The star shows a strong photometric variability interpreted as a possible outburst from EXor type in previous studies. Our photometric data for a period of over six years show a large amplitude variability (ΔV ~ 2.3 mag) and several deep minimums in brightness are observed. The analysis of the collected multicolour photometric data show the typical of UX Ori variables a colour reversal during the minimums in brightness. The observed decreases in brightness have a different shape, and evidences of periodicity are not detected. At the same time, high amplitude rapid variations in brightness typical for the classical T Tauri stars also present on the light curve of GM Cep. The spectrum of GM Cep shows the typical of classical T Tauri stars wide Hα emission line and absorption lines of some metals. We calculate the outer radius of the Hα emitting region as 10.4 ± 0.5 R⊙ and the accretion rate as 1.8 × 10− 7 M⊙ yr− 1.

scholarly journals The correlation between photometric variability and radial velocity jitter

2020 ◽  
Vol 639 ◽  
pp. A35 ◽  
Author(s):  
S. Hojjatpanah ◽  
M. Oshagh ◽  
P. Figueira ◽  
N. C. Santos ◽  
E. M. Amazo-Gómez ◽  
...  
Keyword(s):  
Radial Velocity ◽  
High Precision ◽  
Photometric Observation ◽  
Rotational Period ◽  
Time Intervals ◽  
Photometric Variability ◽  
M Stars ◽  
The Relationship ◽  
K Activity

Context. Characterizing the relation between stellar photometric variability and radial velocity (RV) jitter can help us to better understand the physics behind these phenomena. The current and upcoming high precision photometric surveys such as TESS, CHEOPS, and PLATO will provide the community with thousands of new exoplanet candidates. As a consequence, the presence of such a correlation is crucial in selecting the targets with the lowest RV jitter for efficient RV follow-up of exoplanetary candidates. Studies of this type are also crucial to design optimized observational strategies to mitigate RV jitter when searching for Earth-mass exoplanets. Aims. Our goal is to assess the correlation between high-precision photometric variability measurements and high-precision RV jitter over different time scales. Methods. We analyze 171 G, K, and M stars with available TESS high precision photometric time-series and HARPS precise RVs. We derived the stellar parameters for the stars in our sample and measured the RV jitter and photometric variability. We also estimated chromospheric Ca II H & K activity indicator log(RHK′), v sin i, and the stellar rotational period. Finally, we evaluate how different stellar parameters and an RV sampling subset can have an impact on the potential correlations. Results. We find a varying correlation between the photometric variability and RV jitter as function of time intervals between the TESS photometric observation and HARPS RV. As the time intervals of the observations considered for the analysis increases, the correlation value and significance becomes smaller and weaker, to the point that it becomes negligible. We also find that for stars with a photometric variability above 6.5 ppt the correlation is significantly stronger. We show that such a result can be due to the transition between the spot-dominated and the faculae-dominated regime. We quantified the correlations and updated the relationship between chromospheric Ca II H & K activity indicator log(RHK′) and RV jitter.

scholarly journals Dynamics of wind and the dusty environments in the accreting T Tauri stars RY Tauri and SU Aurigae

2018 ◽  
Vol 483 (1) ◽  
pp. 132-146 ◽  
Author(s):  
P P Petrov ◽  
K N Grankin ◽  
J F Gameiro ◽  
S A Artemenko ◽  
E V Babina ◽  
...  
Keyword(s):  
T Tauri Stars ◽  
Gas Flows ◽  
Photometric Variability ◽  
Outflow Velocity ◽  
T Tauri ◽  
Photometric Observations ◽  
Accretion Model ◽  
Circumstellar Extinction ◽  
Magnetospheric Accretion

Abstract Classical T Tauri stars with ages of less than 10 Myr possess accretion discs. Magnetohydrodynamic processes at the boundary between the disc and the stellar magnetosphere control the accretion and ejections gas flows. We carried out a long series of simultaneous spectroscopic and photometric observations of the classical T Tauri stars, RY Tauri and SU Aurigae, with the aim to quantify the accretion and outflow dynamics at time-scales from days to years. It is shown that dust in the disc wind is the main source of photometric variability of these stars. In RY Tau, we observed a new effect: during events of enhanced outflow, the circumstellar extinction becomes lower. The characteristic time of changes in outflow velocity and stellar brightness indicates that the obscuring dust is near the star. The outflow activity in both stars is changing on a time-scale of years. Periods of quiescence in the variability of the Hα profile were observed during the 2015–2016 period in RY Tau and during the 2016–2017 period in SU Aur. We interpret these findings in the framework of the magnetospheric accretion model, and we discuss how the global stellar magnetic field can influence the long-term variations of the outflow activity.

scholarly journals On the new late B- and early A-type periodic variable stars

2013 ◽  
Vol 9 (S301) ◽  
pp. 43-46
Author(s):  
Nami Mowlavi ◽  
Sophie Saesen ◽  
Fabio Barblan ◽  
Laurent Eyer
Keyword(s):  
Small Amplitude ◽  
Open Cluster ◽  
Variable Stars ◽  
B Stars ◽  
Standard Models

AbstractWe summarize the properties of the new periodic, small-amplitude, variable stars recently discovered in the open cluster NGC 3766. They are located in the region of the Hertzsprung-Russell diagram between δ Sct and slowly pulsating B stars, a region where no sustained pulsation is predicted by standard models. The origin of their periodic variability is currently unknown. We also discuss how the Gaia mission, launched at the end of 2013, can contribute to our knowledge of those stars.

Variable Star Identification in the BATC Field of M67

2005 ◽  
Vol 277-279 ◽  
pp. 869-875
Author(s):  
Hwihyun Kim ◽  
Yong Ik Byun
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Variable Star ◽  
Open Cluster ◽  
Open Clusters ◽  
Eclipsing Binaries ◽  
Photometric Variability ◽  
Phase Dispersion ◽  
Star Identification

We present the result of photometric variability investigation for stars in the field of M67. The old open cluster M67, one of the most studied open clusters, shows the sign of significant main-sequence binary population in its color-magnitude diagrams. Identification of eclipsing binaries and follow-up studies will enable us to study the nature of binary population in most direct manner. We used approximately 350 images from the BATC (Beijing-Arizona-Taipei-Connecticut) data archive to examine variability within one square degree field centered on M67. A total of 18 stars were classified to be real variables. Our new discoveries include seven eclipsing binary systems of which two are likely to be W UMa systems. All of these variables were found using the phase dispersion minimization (PDM) method developed by Shin and Byun[11].

scholarly journals The Rapidly Rotating Giants of the FK Comae-type

1981 ◽  
Vol 93 ◽  
pp. 177-178 ◽  
Author(s):  
B. W. Bopp ◽  
S. M. Rucinski
Keyword(s):  
Radial Velocity ◽  
Spectral Lines ◽  
Photometric Variability ◽  
Double Peaks ◽  
Photometric Observations ◽  
Hα Emission ◽  
Low Mass ◽  
Photometric Period ◽  
Asymmetrically Distributed ◽  
Erratic Behavior

We present new spectroscopic and photometric observations and discuss a small but important group of rapidly rotating G - K giants (FK Com=HD 117555, UZ Lib=BD−8°3999, HD 199178 possibly others) which are photometrically variable, show slightly redshifted and variable Ca II H and K emission and variable Hα emission, show rotationally broadened spectral lines (50–100 km/s), and yet show no large radial velocity variations. Possible explanations of the properties of these stars are discussed and coalescence of a W UMa binary system seems to be the most probable evolutionary state.The most extreme of the group, FK Com is discussed in detail. Its type, G2IIIa (Keenan, priv.comm.) implying MV=−1 (the IR indices are consistent with a giant) suggests a reduction of log g (relative to Sun) −1.5 to −2.5; this can be only marginally reconciled with the dimensions of about 5 Ro resulting from the photometric period 2.4 d. and Vrot sin i about 100 km/s. The photometric variability (0.05 in I, 0.07 in R) is most probably due to spots asymmetrically distributed in longitude. The brightness minima observed by Chugainov in 1966 and 1974 and the new minimum observed in 1979 (JD 2443949.025) can be phased with one period 2.3995±0.0002 d. The erratic behavior of rotationally broadened spectral lines precludes obtaining a radial velocity orbit but an upper limit of 25 km/s for any periodic variations implies that the secondary must be a very low mass object. The strong Hα emission is variable in relative intensity of its double peaks but has a constant full width in excess of 20 A. The full half width at base implies rotational velocities of the order of 570 km/s; the half separation of peaks implies 300 km/s. Existence of an excretion disc of the type suggested by Webbink is possible.

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