scholarly journals The Variability of R, N, and C Stars from HIPPARCOS and AAVSO Data

2000 ◽  
Vol 177 ◽  
pp. 171-178 ◽  
Author(s):  
Michel Grenon ◽  
Janet A. Mattei ◽  
Laurent Eyer ◽  
Grant Foster
Keyword(s):  
Satellite Observations ◽  
Light Curves ◽  
Late Type ◽  
Carbon Stars ◽  
Smooth Curves ◽  
Long Period ◽  
Preliminary Discussion

Accurate photometry was obtained for all program stars during the 3.3-year HIPPARCOS mission. The final observing program included several hundred Mira (M), long-period semiregular (SR), and irregular (L) variables. A detailed calibration of the aging of the optics allowed the evaluation of very precise magnitudes over the whole range of star colors. Since the time coverage of the satellite observations was not sufficient to describe the behavior of M, SR, or L type variables, smooth curves were fitted statistically to the dense AAVSO observations. These curves were then transformed to the HIPPARCOS system in order to complement the HIPPARCOS photometry and thus produce precise light curves with fuller time coverage, for a set of several hundred late-type variables, including most carbon stars brighter than V = 12.4 at minimum luminosity. A preliminary discussion of the behavior of C stars, as observed from space in the broad Hp band, is given.

scholarly journals Variability study of the FBS M giants

2021 ◽  
pp. 478-483
Author(s):  
K. S. Gigoyan ◽  
G. R. Kostandyan
Keyword(s):  
Light Curves ◽  
Late Type ◽  
Data Bases ◽  
Byurakan Survey ◽  
Distance Information ◽  
Long Period ◽  
Sky Survey ◽  
Variability Study ◽  
Variability Data ◽  
Galactic Distribution

We study in this paper variability of the late-type M giants found in the First Byurakan Survey (FBS) spectroscopic data base. We used phase dependent light – curves from large sky area variability data bases such as Catalina Sky Survey (CSS) and All-Sky Automated Survey for Supernovae (ASAS-SN). We used also the distance information derived from Gaia EDR3 to construct the Galactic distribution of the M – type giants from the second edition of the FBS Late-Type Stars catalogue including various kinds of long period variables.

scholarly journals Monitoring active stars 29 Dra, 12 Cam and colour excess of II Peg

2007 ◽  
pp. 51-56
Author(s):  
M. Zboril
Keyword(s):  
High Latitude ◽  
Colour Index ◽  
Light Curves ◽  
Late Type ◽  
Long Period ◽  
Colour Excess ◽  
Active Stars

We present the BV light curves analysis of late-type, long-period stars 29 Dra, 12 Cam for the season 2005/2006, and shorter-period star II Peg for the same season. High latitude spots (alternatively spot configuration) cooler than surrounding photosphere were able to explain the light curves. The II Peg colour- index shift in H-R diagram is probably a consequence of stellar metallicity. Other associated mechanisms are briefly discussed.

scholarly journals Discovery of a second pulsating intermediate helium-enriched sdOB star

2019 ◽  
Vol 623 ◽  
pp. L12 ◽  
Author(s):  
M. Latour ◽  
E. M. Green ◽  
G. Fontaine
Keyword(s):  
Galactic Halo ◽  
Local Thermodynamic Equilibrium ◽  
Variable Stars ◽  
Light Curves ◽  
Atmospheric Parameters ◽  
Instability Strip ◽  
Long Period ◽  
Non Local ◽  
Halo Population ◽  
Low Amplitude

We present the discovery of long-period, low-amplitude, g-mode pulsations in the intermediate He-rich hot subdwarf (sdOB) star Feige 46. So far, only one other He-enriched sdOB star (LS IV−14 ° 116) was known to exhibit such pulsations. From our ground-based light curves of Feige 46, we extracted five independent periodicities ranging from 2294 s to 3400 s. We fit our optical spectrum of the star with our grid of non-local thermodynamic equilibrium (NLTE) model atmospheres and derived the following atmospheric parameters: Teff = 36120 ± 230 K, log g = 5.93 ± 0.04, and log N(He)/N(H) = −0.32 ± 0.03 (formal fitting errors only). These parameters are very similar to those of LS IV−14 ° 116 and place Feige 46 well outside of the instability strip where the hydrogen-rich g-mode sdB pulsators are found. We used the Gaia parallax and proper motion of Feige 46 to perform a kinematic analysis of this star and found that it likely belongs to the Galactic halo population. This is most certainly an intriguing and interesting result given that LS IV−14 ° 116 is also a halo object. The mechanism responsible for the pulsations in these two peculiar objects remains unclear, but a possible scenario involves the ϵ-mechanism. Although they are the only two members in their class of variable stars, these pulsators appear to have more in common than just their pulsation properties.

scholarly journals The Galactic Distribution of OH/IR Stars

1977 ◽  
Vol 42 ◽  
pp. 399-433
Author(s):  
H.J. Habing
Keyword(s):  
Present Status ◽  
Line Emission ◽  
Microwave Line ◽  
Late Type ◽  
Maser Emission ◽  
Long Period ◽  
Ir Stars ◽  
Long Period Variables ◽  
Recent Compilation ◽  
Galactic Distribution

In 1967 Wilson and Barrett (1968, 1970) discovered that some long period variables, very red and apparently very late type stars, emit OH microwave line emission that is especially strong in the 1612 MHz line at 18 cm. At present some 65 such OH-emitting stars have been identified - for a recent compilation see Bowers and Kerr (1977, M giants) and Baudry et al. (1977, M supergiants). Several stars show maser emission in H2O and SiO as well. At this colloquium Winnberg will review the present status of our knowledge of these stars.

scholarly journals Photometry of the Recent Eclipse of Epsilon Aurigae

1986 ◽  
Vol 7 ◽  
pp. 142-149
Author(s):  
Robert E. Stencel
Keyword(s):  
Light Curves ◽  
Optical Polarization ◽  
Infrared Photometry ◽  
Ultraviolet Spectrophotometry ◽  
Long Period ◽  
Epsilon Aurigae

AbstractNew observations of the long period eclipsing system Epsilon Aurigae are discussed, including optical and infrared photometry, ultraviolet spectrophotometry and optical polarization. Trends are noted in the light curves and compared to previous eclipses. Comments regarding interpretation are also provided.

scholarly journals Activity and rotation of the X-ray emitting Kepler stars

2019 ◽  
Vol 628 ◽  
pp. A41 ◽  
Author(s):  
D. Pizzocaro ◽  
B. Stelzer ◽  
E. Poretti ◽  
S. Raetz ◽  
G. Micela ◽  
...  
Keyword(s):  
White Light ◽  
Main Sequence ◽  
Magnetic Activity ◽  
Light Curves ◽  
Late Type ◽  
Main Sequence Stars ◽  
Photometric Variability ◽  
X Ray ◽  
Rotation Periods ◽  
Flare Frequency

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation-activity studies found in the literature suffer from inhomogeneity in the measurement of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting, late-type main-sequence stars observed by XMM-Newton and Kepler. We measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 20 of which do not have period reported in the previous literature. In the X-ray activity-rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~10 d but it can be probed only marginally with this sample, which is biased towards fast rotators due to the X-ray selection. We observe seven bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~0.15 d−1, consistent with the optical flare frequency obtained from the much longer Kepler time-series.

scholarly journals Detecting activity cycles of late-type dwarfs in Kepler data

2013 ◽  
Vol 9 (S302) ◽  
pp. 224-227
Author(s):  
Krisztián Vida ◽  
Katalin Oláh
Keyword(s):  
Active Region ◽  
Frequency Analysis ◽  
Rotation Period ◽  
Light Curves ◽  
Late Type ◽  
Dwarf Stars ◽  
Time Frequency ◽  
Activity Cycles ◽  
Using Data ◽  
Fast Rotating

AbstractUsing data of fast-rotating active dwarf stars in the Kepler database, we perform time-frequency analysis of the light curves in order to search for signs of activity cycles. We use the phenomenon that the active region latitudes vary with the cycle (like the solar butterfly diagram), which causes the observed rotation period to change as a consequence of differential rotation. We find cycles in 8 cases of the 39 promising targets with periods between of 300–900 days.

scholarly journals A search for transiting planets around FGKM dwarfs and subgiants in the TESS full frame images of the Southern ecliptic hemisphere

2020 ◽  
Vol 498 (2) ◽  
pp. 1726-1749 ◽  
Author(s):  
M Montalto ◽  
L Borsato ◽  
V Granata ◽  
G Lacedelli ◽  
L Malavolta ◽  
...  
Keyword(s):  
Random Forest ◽  
Light Curves ◽  
Correct Identification ◽  
Transiting Planets ◽  
Long Period ◽  
Period Distribution ◽  
Distribution Ranges ◽  
Show Evidence ◽  
Dynamical Constraints ◽  
Subgiant Stars

ABSTRACT In this work, we present the analysis of 976 814 FGKM dwarf and subgiant stars in the Transiting Exoplanet Survey Telescope (TESS) full frame images (FFIs) of the Southern ecliptic hemisphere. We present a new pipeline, DIAmante, developed to extract optimized, multisector photometry from TESS FFIs and a classifier, based on the Random Forest technique, trained to discriminate plausible transiting planetary candidates from common false positives. A new statistical model was developed to provide the probability of correct identification of the source of variability. We restricted the planet search to the stars located in the least crowded regions of the sky and identified 396 transiting planetary candidates among which 252 are new detections. The candidates’ radius distribution ranges between 1 R⊕ and 2.6 RJ with median value of 1 RJ and the period distribution ranges between 0.25 and 105 d with median value of 3.8 d. The sample contains four long period candidates (P > 50 d), one of which is new, and 64 candidates with periods between 10 and 50 d (42 new ones). In the small planet radius domain (4R < R⊕), we found 39 candidates among which 15 are new detections. Additionally, we present 15 single transit events (14 new ones), a new candidate multiplanetary system, and a novel candidate around a known TOI. By using Gaia dynamical constraints, we found that 70 objects show evidence of binarity. We release a catalogue of the objects we analysed and the corresponding light curves and diagnostic figures through the MAST and ExoFOP portals.

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