scholarly journals Red variables in the OGLE-II database: first results for the LMC

2004 ◽  
Vol 193 ◽  
pp. 55-59
Author(s):  
L.L. Kiss ◽  
T.R. Bedding
Keyword(s):  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Red Giants ◽  
Period Analysis ◽  
Short Period ◽  
First Results ◽  
Red Giant ◽  
Single Epoch ◽  
Low Amplitude ◽  
Radial Pulsations

AbstractWe present a period analysis of more then 23 000 red giants in the Large Magellanic Cloud observed by the OGLE-II microlensing project. Periods combined with the single-epoch 2MASS J H KS magnitudes revealed the complex distributions of stars in the period-luminosity plane. Besides four different sequences corresponding to different modes of pulsation in AGB stars, we also discovered two distinct and well-separated sequences below the tip of the Red Giant Branch, consisting of almost 10000 short-period and low-amplitude red variable stars. We propose that the majority are likely to be first ascent red giants, showing radial pulsations in the second and third overtone modes.

scholarly journals The Magellanic Edges Survey I: Description and first results

2020 ◽  
Vol 497 (3) ◽  
pp. 3055-3075
Author(s):  
L R Cullinane ◽  
A D Mackey ◽  
G S Da Costa ◽  
S E Koposov ◽  
V Belokurov ◽  
...  
Keyword(s):  
Target Selection ◽  
Radial Distance ◽  
Large Magellanic Cloud ◽  
Disc Model ◽  
Observation Strategy ◽  
First Results ◽  
Mass Estimate ◽  
Red Clump ◽  
Red Giant ◽  
Giant Branch Stars

ABSTRACT We present an overview of, and first science results from, the Magellanic Edges Survey (MagES), an ongoing spectroscopic survey mapping the kinematics of red clump and red giant branch stars in the highly substructured periphery of the Magellanic Clouds. In conjunction with Gaia astrometry, MagES yields a sample of ~7000 stars with individual 3D velocities that probes larger galactocentric radii than most previous studies. We outline our target selection, observation strategy, data reduction, and analysis procedures, and present results for two fields in the northern outskirts (>10° on-sky from the centre) of the Large Magellanic Cloud (LMC). One field, located in the vicinity of an arm-like overdensity, displays apparent signatures of perturbation away from an equilibrium disc model. This includes a large radial velocity dispersion in the LMC disc plane, and an asymmetric line-of-sight velocity distribution indicative of motions vertically out of the disc plane for some stars. The second field reveals 3D kinematics consistent with an equilibrium disc, and yields Vcirc = 87.7 ± 8.0 km s−1 at a radial distance of ~10.5 kpc from the LMC centre. This leads to an enclosed mass estimate for the LMC at this radius of (1.8 ± 0.3) × 1010 M⊙.

scholarly journals Spectroscopy of Overluminous Cepheids in the Magellanic Clouds

1984 ◽  
Vol 108 ◽  
pp. 223-224
Author(s):  
Horace A. Smith ◽  
Leo Connolly
Keyword(s):  
Globular Cluster ◽  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Small Magellanic Cloud ◽  
Single Star ◽  
Rr Lyrae ◽  
Short Period ◽  
The Galaxy

The Small Magellanic Cloud is known to contain types of short period Cepheid variable stars not yet discovered in either the Large Magellanic Cloud or, with the exception of a single star, in the Galaxy. These variables can be divided into two categories: anomalous Cepheids and Wesselink-Shuttleworth (WS) stars. The former, which have also been found in dwarf spheroidal systems and in the globular cluster NGC 5466, have periods of 0.4–3 days, but average 0.7–1.0 mag. brighter than RR Lyrae and BL Her stars of equal period. The stars we call WS stars have periods less than about 1.1 day and, at MV = −1 to −2, are brighter than anomalous Cepheids of equal period.

scholarly journals AKARI IRC survey of the Large Magellanic Cloud: A new feature in the infrared color—magnitude diagram

2008 ◽  
Vol 4 (S256) ◽  
pp. 9-13
Author(s):  
Yoshifusa Ita ◽  
Takashi Onaka ◽  
Daisuke Kato ◽  
Keyword(s):  
Infrared Camera ◽  
Large Magellanic Cloud ◽  
Emission Feature ◽  
Magellanic Cloud ◽  
Circumstellar Dust ◽  
Red Giants ◽  
Broad Emission ◽  
Magnitude Diagram ◽  
Red Giant ◽  
New Feature

AbstractWe observed an area of 10 deg2 of the Large Magellanic Cloud using the Infrared Camera on board AKARI. The observations were carried out using five imaging filters (3, 7, 11, 15, and 24 μm) and a dispersion prism (2 − 5 μm, λ/Δλ ~ 20) equipped in the IRC. The 11 and 15 μm data, which are unique to AKARI IRC, allow us to construct color-magnitude diagrams that are useful to identify stars with circumstellar dust. We found a new sequence in the color-magnitude diagram, which is attributed to red giants with luminosity fainter than that of the tip of the first red giant branch. We suggest that this sequence is likely to be related to the broad emission feature of aluminium oxide at 11.5 μm.

scholarly journals Molecular Masers in Variable Stars

2002 ◽  
Vol 19 (4) ◽  
pp. 499-504 ◽  
Author(s):  
Georgij M. Rudnitskij
Keyword(s):  
Line Emission ◽  
Variable Stars ◽  
Circumstellar Envelope ◽  
Red Giants ◽  
Circumstellar Envelopes ◽  
Emission Data ◽  
Physical Mechanisms ◽  
Stellar Pulsations ◽  
Red Giant ◽  
Maser Radio

AbstractWhen a star with a mass of one to a few solar masses enters the red giant stage of its evolution, the radius of its atmosphere reaches several astronomical units. Pulsational instability is typical for this stage. Most stars become Mira-type or semiregular variables with light cycles of a few hundred days. Red giants lose mass at a rate M = 10−7−10−5M⊙ yr−1. Extensive gas–dust circumstellar envelopes form. These envelopes contain various molecular species. Some of these molecules (OH, H2O, SiO, HCN) manifest themselves in maser radio emission. Data on the H2O maser variability and its connection with the stellar brightness variations are discussed. In the H2O line circumstellar masers can be divided into ‘stable’ (showing persistent emission — R Aql, U Her, S CrB, X Hya) and ‘transient’ (appearing in the H2O line once per 10–15 stellar light cycles — R Leo, R Cas, U Aur). Physical mechanisms of the maser variability are discussed. The most probable process explaining the observed visual–H2O correlation is the influence of shock waves on the masing region. Usually it is assumed that shocks in Mira atmospheres are driven by stellar pulsations. Here an alternative explanation is proposed. If a star during its main sequence life possessed a planetary system, similar to the solar system, the planets will be embedded in a rather dense and hot medium. Effects of a planet revolving around a red giant at a short distance (inside its circumstellar envelope) are discussed. A shock produced by the supersonic motion of a planet can account for the correlated variability of the Hα line emission and H2O maser. If the planetary orbit is highly eccentric, then the connected Hα–H2O flare episodes may be explained by the periastron passage of the planet. New tasks for the upgraded ATCA are discussed.

scholarly journals Oscillations of HB Red Variable Stars

1998 ◽  
Vol 185 ◽  
pp. 401-402
Author(s):  
D.R. Xiong ◽  
Q. L. Cheng ◽  
L. Deng
Keyword(s):  
Globular Clusters ◽  
Turbulent Viscosity ◽  
Variable Stars ◽  
Instability Strip ◽  
Rr Lyrae ◽  
Short Period ◽  
Spatial Oscillations ◽  
The Right ◽  
Thermodynamic Coupling ◽  
Low Amplitude

Using a nonlocal time-dependent theory of convection, we have calculated the linear non-adiabatic oscillations of the Horizontal Branch (HB) stars, with both the dynamic and thermodynamic coupling between convection and oscillations been carefully treated. Turbulent pressure and turbulent viscosity have been included consistently in our equations of non-adiabatic pulsation. When the coupling between convection and oscillations is ignored, for all models with Te ≤ 7350K, the fundamental through the second overtone are pulsationally unstable; while for Te ≤ 6200K all the models are unstable up to (at least) the 9th overtone. When the coupling between convection and oscillations is included, the RR Lyrae instability strip is very well predicted. Within the strip most models are pulsationally unstable only for the fundamental and the first few overtones. Turbulent viscosity is an important damping mechanism. Being exclusively distinct from the luminous red variables (long period variables), the HB stars to the right of the RR Lyrae strip are pulsationally stable for the fundamental and low-order overtones, but become unstable for some of the high-order overtones. This may provide a valuable clue for the short period, low amplitude red variables found outside the red edge of the RR Lyrae strip on the H-R diagram of globular clusters. Moreover, we present a new radiation modulated excitation mechanism functioning in radiation flux gradient regions. The effects of nonlocal convection and the dynamic coupling between convection and oscillations are discussed. The spatial oscillations of the thermal variables in the pulsational calculations have been effectively suppressed.

scholarly journals The OmegaWhite survey for short-period variable stars – I. Overview and first results

2015 ◽  
Vol 454 (1) ◽  
pp. 507-530 ◽  
Author(s):  
S. A. Macfarlane ◽  
R. Toma ◽  
G. Ramsay ◽  
P. J. Groot ◽  
P. A. Woudt ◽  
...  
Keyword(s):  
Variable Stars ◽  
Short Period ◽  
First Results ◽  
Period Variable

Breaking the age–metallicity degeneracy: The metallicity distribution and star formation history of the Large Magellanic Cloud

2008 ◽  
Vol 4 (S256) ◽  
pp. 263-268 ◽  
Author(s):  
Andrew A. Cole ◽  
Aaron J. Grocholski ◽  
Doug Geisler ◽  
Ata Sarajedini ◽  
Verne V. Smith ◽  
...  
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Large Magellanic Cloud ◽  
Star Formation History ◽  
Red Giants ◽  
Formation History ◽  
History Of ◽  
Red Giant ◽  
Metallicity Distribution ◽  
Modelling Process

AbstractWe have obtained metallicities from near-infrared calcium triplet spectroscopy for nearly a thousand red giants in 28 fields spanning a range of radial distances from the center of the bar to near the tidal radius. We have used these data to investigate the radius-metallicity and age-metallicity relations. A powerful application of these data is in conjunction with the analysis of deep HST color–magnitude diagrams (CMDs). Most of the power in determining a robust star-formation history from a CMD comes from the main-sequence turnoff and subgiant branches. The age-metallicity degeneracy that results is largely broken by the red giant branch color, but theoretical model RGB colors remain uncertain. By incorporating the observed metallicity distribution function into the modelling process, a star-formation history with massively increased precision and accuracy can be derived. We incorporate the observed metallicity distribution of the LMC bar into a maximum-likelihood analysis of the bar CMD, and present a new star formation history and age–metallicity relation for the bar. The bar is certainly younger than the disk as a whole, and the most reliable estimates of its age are in the 5–6 Gyr range, when the mean gas abundance of the LMC had already increased to [Fe/H] ≳ −0.6. There is no obvious metallicity gradient among the old stars in the LMC disk out to a distance of 8–10 kpc, but the bar is more metal-rich than the disk by ≈0.1–0.2 dex. This is likely to be the result of the bar's younger average age. In both disk and bar, 95% of the red giants are more metal-rich than [Fe/H] = −1.2.

scholarly journals The Characteristics of the Field RR Lyrae Stars in the Magellanic Clouds

1974 ◽  
Vol 59 ◽  
pp. 107-108
Author(s):  
J. A. Graham
Keyword(s):  
Stellar Evolution ◽  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Light Curves ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
First Results ◽  
Lyrae Stars

The Magellanic Clouds are well known as being very suitable for observing the various stages of stellar evolution. During the last few years, I have been studying the RR Lyrae variable stars in each of the two Clouds. Some first results were reported at IAU Colloquium No. 21 in 1972 (Graham, 1973). Here, I would like to update these results on the basis of more recent data and to comment on some of the characteristics of the field RR Lyrae stars in each system. Periods and light curves are now available for 63 RR Lyrae stars in a 1° x 1.3° field centered on the cluster NGC 1783 in the Large Magellanic Cloud (LMC) and for 62 stars in a 1° x 1.3° field centered on the cluster NGC 121 in the Small Magellanic Cloud (SMC). Both ab and c type variables are represented and, viewed individually, the Cloud RR Lyraes are identical in characteristics to those known in our Galaxy. Studied as groups, however, there are small but significant differences between the RR Lyrae stars in each system. The following four specific features seem to be emerging from the study.

Core Helium Burning Evolution at 5M⊙

1971 ◽  
Vol 2 (1) ◽  
pp. 24-25
Author(s):  
J. W. Robertson
Keyword(s):  
Effective Temperature ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Red Giants ◽  
Helium Burning ◽  
Red Giant

Observations of the red giants in NGC 1866 in the Large Magellanic Cloud, made by Arp and Thackeray provide a strict test for core helium burning models of about 5M⊙. The main observational features to be reproduced theoretically are the luminosity of the red giants, the range in effective temperature that they occupy and the ratio of the number of giants near the blue end of this range to the number at the bottom of the red giant branch. Meyer-Hofmeister attempted a theoretical fit to these observations using the initial (X, Y, Z) composition (0.602, 0.354, 0.044) and assuming the stars to have formed uniformly over a period of 1.5 × 107 years about a mean age of 5.75 × 107 years. Although she was able to fit the luminosity and effective temperature spread of the red giants, her theory predicted far too many stars at the bottom of the red giant branch relative to the number of bluer giants.

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