Dynamical chromospheric structure of α orionis

Querci, M.; Querci, F.

doi:10.1007/3-540-16763-3_245

Cited by 12 publications

(14 citation statements)

References 9 publications

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“…This explanation for semiregular behaviour has been suggested before by several authors (see Querci 1986). While we cannot exclude that an interpretation of the light change by the coupling of two periods may be correct for selected SRVs, we think that our investigation has outlined three severe problems in this context: On the one hand, we found that the light change can be nicely fit with a few periods over a relatively short time scale of a few cycles.…”

Section: Discussionsupporting

confidence: 77%

Multi-colour light variation of AGB stars observed with ISO

Kerschbaum¹,

Lebzelter²,

Lázaro

2001

A&A

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Abstract. New visual light curves and infrared multi-epoch photometry are presented for a sample of AGBstars spectroscopically observed with ISO. While the ISO work is or will be presented elsewhere, the aim of this paper is to give an overview of the properties of the light change of the objects. This information is crucial for the interpretation of the valuable ISO material. Using the University of Vienna Twin Automatic Photoelectric Telescope (APT) we monitored the stars of our sample in the photometric bands V and IC. We present the light curve of each object and derive the parameters of the current light change, such as period(s) and amplitude. Furthermore we give V −IC colours and colour variations for these objects. Our results allow us to derive some general results on semiregular and irregular variables. Only in less than 50% of the cases could we confirm the GCVS period. Moreover, we did not find any pronounced difference between SRb and Lb variables in the regularity of the light curve. The existence of rapid oscillations indicated by Hipparcos data could not be confirmed. In addition to the visual light changes we present new near infrared photometry data. Although typically only few data points are available, they can be viewed relative to the better-monitored visual light curves providing information on possible phase shifts and differences in amplitude in different parts of the spectrum. Furthermore, multi-epoch photometry allows us to derive mean colours for these objects.

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Section: Discussionsupporting

confidence: 77%

Multi-colour light variation of AGB stars observed with ISO

Kerschbaum¹,

Lebzelter²,

Lázaro

2001

A&A

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“…For this reason, sometimes the M stars are referred to as oxygen stars in contrast to the carbon stars. Still other abundance parameters (e.g., metallicity and enhancements of s-process elements: Sr, Y, Zr, and Ba) are seen in the spectra of numerous cool stars (Querci 1986). …”

Section: Emission Starsmentioning

confidence: 99%

“…The C and O atoms are fully trapped in CO, with ratios between 0.98 and 1.02. Consequently, the S stars are rare because only a few stars have (C/O) % 1 (Querci 1986).…”

Section: And S Starsmentioning

confidence: 99%

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Galactic Distributions and Statistics of the HD Stars in the Michigan Spectral Catalogue

2007

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The systematic, spectroscopic two-dimensional classification of the HD stars by N. H. is approximately three-quarters complete. Over 161,000 stars have been classified visually using 10 objective-prism plates (2 8 resolution) taken at CTIO with the Michigan Curtis Schmidt telescope. The published portion of this large, homogeneous database, taken from volumes 1-5 of the Michigan Spectral Catalogue (declination À90 to +5 ), has been used to investigate the Galactic (l, b) distributions of the objects primarily via Aitoff equal-area projection plots. Particular attention has been given to the normal dwarfs and giants, the supergiants, and many of the spectroscopically peculiar classes of stars, such as the WR, Be, shell, Ap, Am, Del, C, S, CH, Ba, and CN stars.

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“…The six stars were a Ari, a Tau, (3 Gem, a Hya, a Boo and E Peg 4 Temperatures of over 20000 K are needed for this line to form and densities of over needed for the line to be in emission rather than absorption (see Querci [136] page 138) 5 For more details on non-radial pulsation, particularly p and g modes, see §2.3.5 electrons per cm 3 are…”

Section: The History Of Radial-velocity Variation In K Giantsmentioning

confidence: 99%

High precision radial-velocity measurements of late-type evolved stars

Cummings¹,

Hearnshaw²,

Kilmartin³

et al. 1999

International Astronomical Union Colloquium

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Late-type evolved stars include the variable red giants, like Mira and semi-regular variables, and the pulsating supergiant RV Tauri stars. Despite this, K-type giants in the past were generally believed to be constant in photometry and radial velocity, but in the last decade it has been discovered that this is not necessarily the case. This was the motivation for spectroscopic observations of 44 late-type evolved stars to be carried out over three years, in the hope of helping to determine how common K giants variable in radial velocity are and whether the variations are related to those seen for other late-type evolved stars.The observations were obtained at Mount John University Observatory and used with digital crosscorrelation to achieve relative radial velocities of 50 m/s precision. At this precision all but eight of the observed stars were found to be variable in radial velocity. Thirteen stars also had broad-band photometry taken, because any one of orbital motion, rotation with starspots, pulsation and the motion of large convective cells could cause apparent radial-velocity variations. Knowledge of the relationship between light and radial-velocity variations can help distinguish between these different mechanisms.The timescales for these different mechanisms were also estimated to help determine which was responsible for the variations observed. Generally the observed K-giant radial-velocity timescales were of the order of a few hundred days, which indicates they are due to one of binary motion, rotational modulation or non-acoustic non-radial pulsation. However, forM giants and supergiants the situation was very different with both short-term and long-term radial-velocity timescales being found in most stars. In most cases the short-term timescale is due to acoustic pulsation, while the long-term timescale could be due to any one of binary motion, surface features (including the motion of large convective cells) or non-acoustic non-radial pulsation.ii

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Dynamical chromospheric structure of α orionis

Cited by 12 publications

References 9 publications

Multi-colour light variation of AGB stars observed with ISO

Multi-colour light variation of AGB stars observed with ISO

Galactic Distributions and Statistics of the HD Stars in the Michigan Spectral Catalogue

High precision radial-velocity measurements of late-type evolved stars

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