We present measurements of the fluorine abundance in a Galactic bulge asymptotic giant branch (AGB) star. The measurements were performed using high-resolution K-band spectra obtained with the CRIRES ...spectrograph, which has been recently installed at ESO's VLT, together with state-of-the- art model atmospheres and synthetic spectra. This represents the first fluorine abundance measurement in a Galactic bulge star, and one of few measurements of this kind in a third dredge-up oxygen-rich AGB star. The F abundance is found to be close to the solar value scaled down to the metallicity of the star, and in agreement with disk giants that are comparable to the bulge giant studied here. The measurement is of astrophysical interest also because the star's mass can be estimated rather accurately. AGB nucleosynthesis models predict only a very mild enrichment of F in such low mass AGB stars. Thus, we suggest that the fluorine abundance found in the studied star is representative for the star's natal cloud, and that fluorine must have been produced at a similar level in the bulge and in the disk.
Aims.We investigated the cloud of ejecta resulting from the mass loss associated with the final helium shell flash in V605 Aql. Methods.V605 Aql was imaged at high spatial resolution in both optical ...emission lines and the infrared continuum using HST/WFPC2 and Gemini/Hokupa'a+QUIRC, respectively. The He I 10 830 Å spectrum was also observed. Results.The obscuring circumstellar shell, whose effects were first seen in 1923, is shown to be a disk with extended structure, including knots. The morphology of the V605 Aql circumstellar shell is discussed as an 80 year old in an evolutionary sequence consisting of recent, as well as much older, final flash objects. Conclusions.The obscuration of V605 Aql by dust marked the emergence of the hot white dwarf remnant from an optically thick pseudo-photosphere. This white dwarf drives a 2500 km s-1 wind principally in one plane resulting in a circumstellar disk. Where the wind encounters the circumstellar disk, He I 10 830 Å emission is created, and hot, ~1500 K, grains are generated. Grains exit the disk at 350 K, and the accompanying gas then expands at ~140 km s-1. The strong concentration of the mass loss to the disk suggests the white dwarf is now rotating rapidly. There is convincing evidence in the literature that this process is also seen in V4334 Sgr and is still going on in the old final flash objects A30 and A78.
We compare velocities from near infrared lines with center-of-mass velocities for a sample of semiregular and irregular variables to search for indications for a convective blueshift. It is shown ...that a general blueshift is present but that the light variability is obviously not dominated by convective cells but rather by stellar pulsation. All stars of our sample show a similar shape and amplitude in the velocity variations. Long secondary periods are a common feature in these objects and strongly influence the measured velocity shifts. The star V366 Aql is found to be the first SRV showing line doubling.
We present near infrared velocity curves for 12 long period variables (LPVs) in the globular cluster 47 Tuc (NGC 104). New light curves are also presented for these variables. Results are compared ...with the period-luminosity sequences occupied by the LPVs in the LMC. Sequence C variables (fundamental mode pulsators) have larger velocity amplitudes than sequence B variables (first overtone pulsators). We show that, at similar luminosities, higher mass loss rates are associated with larger pulsation amplitudes. One variable (V18) does not fit the normal period luminosity sequences and it has an unusually large amount of circumstellar dust, suggesting that it has recently undergone a thermal pulse on the AGB. Finally, we report the discovery of three new long period variable stars in the cluster core, all previously found to have a large infrared excess.
We analysed the light curves of a large sample of long period variables in the LMC from the AGAPEROS catalogue. The (non)regularity of the light change is discussed in detail showing that the ...majority of the light curves cannot be described properly by a single period. We show that semiregular and small amplitude variability do not necessarily correlate as has been assumed in several previous studies. Using near-infrared data from the DENIS survey we correlate the light change with colours and luminosities of the objects. These results are used to compare long period variables in the LMC with LPVs in the Galactic Bulge and in the solar neighborhood. This work is based on data collected by the EROS and DENIS collaborations.
Gaia Data Release 3 Lebzelter, T.; Mowlavi, N.; Lecoeur-Taibi, I. ...
Astronomy and astrophysics (Berlin),
06/2023, Letnik:
674
Journal Article
Recenzirano
Odprti dostop
Context.
The third
Gaia
Data Release covers 34 months of data and includes the second
Gaia
catalogue of long-period variables (LPVs), with
G
variability amplitudes larger than 0.1 mag (5–95% quantile ...range).
Aims.
The paper describes the production and content of the second
Gaia
catalogue of LPVs and the methods we used to compute the published variability parameters and identify C-star candidates.
Methods.
We applied various filtering criteria to minimise contamination from variable star types other than LPVs. The period and amplitude of the detected variability were derived from model fits to the
G
-band light curve wherever possible. C stars were identified using their molecular signature in the low-resolution RP spectra.
Results.
The catalogue contains 1 720 558 LPV candidates, including 392 240 stars with published periods (ranging from 35 to ∼1000 days) and 546 468 stars classified as C-star candidates. Comparison with literature data (OGLE and ASAS-SN) leads to an estimated completeness of 80%. The recovery rate is about 90% for the most regular stars (typically miras) and 60% for SRVs and irregular stars. At the same time, the number of known LPVs is increased by a factor of 6 with respect to literature data for amplitudes larger than 0.1 mag in
G
, and the contamination is estimated to be below 2%. Our C-star classification, based on solid theoretical arguments, is consistent with spectroscopically identified C stars in the literature. Caution must be taken in crowded regions, however, where the signal-ro-noise ratio of the RP spectra can become very low, or if the source is reddened by some kind of extinction. The quality and potential of the catalogue are illustrated by presenting and discussing LPVs in the solar neighbourhood, in globular clusters, and in galaxies of the Local Group.
Conclusions.
This is the largest all-sky LPVs catalogue to date. The photometric depth reaches
G
= 20 mag. This is a unique dataset for research into the late stages of stellar evolution.
Gaia Data Release 2 Mowlavi, N.; Lecoeur-Taïbi, I.; Lebzelter, T. ...
Astronomy and astrophysics (Berlin),
10/2018, Letnik:
618
Journal Article
Recenzirano
Odprti dostop
Context. Gaia
Data Release 2 (DR2) provides a unique all-sky catalogue of 550 737 variable stars, of which 151 761 are long-period variable (LPV) candidates with
G
variability amplitudes larger than ...0.2 mag (5–95% quantile range). About one-fifth of the LPV candidates are Mira candidates, the majority of the rest are semi-regular variable candidates. For each source,
G
,
G
BP
, and
G
RP
photometric time-series are published, together with some LPV-specific attributes for the subset of 89 617 candidates with periods in
G
longer than 60 days.
Aims.
We describe this first
Gaia
catalogue of LPV candidates, give an overview of its content, and present various validation checks.
Methods.
Various samples of LPVs were used to validate the catalogue: a sample of well-studied very bright LPVs with light curves from the American Association of Variable Star Observers that are partly contemporaneous with
Gaia
light curves, a sample of
Gaia
LPV candidates with good parallaxes, the All-Sky Automated Survey for Supernovae catalogue of LPVs, and the Optical Gravitational Lensing Experiment (OGLE) catalogues of LPVs towards the Magellanic Clouds and the Galactic bulge.
Results.
The analyses of these samples show a good agreement between
Gaia
DR2 and literature periods. The same is globally true for bolometric corrections of M-type stars. The main contaminant of our DR2 catalogue comes from young stellar objects (YSOs) in the solar vicinity (within ~1 kpc), although their number in the whole catalogue is only at the percent level. A cautionary note is provided about parallax-dependent LPV attributes published in the catalogue.
Conclusions.
This first
Gaia
catalogue of LPVs approximately doubles the number of known LPVs with amplitudes larger than 0.2 mag, despite the conservative candidate selection criteria that prioritise low contamination over high completeness, and despite the limited DR2 time coverage compared to the long periods characteristic of LPVs. It also contains a small set of YSO candidates, which offers the serendipitous opportunity to study these objects at an early stage of the
Gaia
data releases.
Context.
The period-luminosity diagram (PLD) has proven to be a powerful tool for studying populations of pulsating red giants.
Gaia
Data Release 2 (DR2) provides a large data set including many ...long-period variables (LPVs) on which this tool can be applied.
Aims.
We investigate the location of LPVs from the Large and Small Magellanic Clouds in the PLD using various optical and infrared luminosity indicators from
Gaia
and 2MASS, respectively. We thereby distinguish between stars of different masses and surface chemistry.
Methods.
The data set taken from the
Gaia
DR2 catalogue of LPVs allows for a homogeneous study from low- to high-mass LPVs. These sources are divided into sub-populations of asymptotic giant branch (AGB) stars according to their mass and their O- or C-rich nature using the
Gaia
-2MASS diagram developed by our group. This diagram uses a Wesenheit index
W
BP, RP
based on Wesenheit functions in the
Gaia
and 2MASS photometric bands. Four different luminosity indicators are used to study the period-luminosity (P–L) relations.
Results.
We provide the first observational evidence of a P–L relation offset for both fundamental and 1O pulsators between low- and intermediate-mass O-rich stars, in agreement with published pulsation predictions. Among the luminosity indicators explored, sequence C′ is the narrowest in the
P
–
W
BP, RP
diagram, and is thus to be preferred over the other PLDs for the determination of distances using LPVs. The majority of massive AGB stars and red supergiants form a smooth extension of sequence C of low- and intermediate-mass AGB stars in the
P
–
W
BP, RP
diagram, suggesting that they pulsate in the fundamental mode. All results are similar in the two Magellanic Clouds.
In this paper we present radial velocity curves of AGB variables that exhibit various kinds of anomalies: semiregular variables (SRVs) with typical mira periods, SRVs exceeding the mira 2.5 mag ...amplitude limit, miras with secondary maxima in their light curves, and a SRV with a long secondary period. The stars with reliable Hipparcos parallaxes from this and from previous studies are plotted in a $\log P{-}M_{K}$-diagram. Our objects nicely follow the $\log P{-}M_{K}$-relations determined for the LMC. This allows the pulsation mode to be identified. While all miras fall on the fundamental mode sequence, the SRVs fall on both the first overtone and fundamental mode sequences. The SRVs on the fundamental mode sequence occur at both high and low luminosities, some of them being more luminous than larger amplitude miras. This demonstrates observationally that some parameter other than luminosity affects the stability of long period variables, probably mass. First overtone pulsators all show velocity amplitudes around 4 km s-1. For the fundamental mode pulsators, the velocity amplitude shows a correlation with light amplitude. The two miras R Cen and R Nor, known for their double-peaked light curves, have velocity curves that are quite different. The R Nor velocity curve shows no evidence of the double peaks, meaning that the true pulsation period is the time between alternate minima or maxima. There is slight evidence for a double bump in the R Cen velocity curve. It is suggested that these stars are relatively massive (3–5 $M_{\odot}$).
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