scholarly journals Optical Spectroscopy of Six Carbon-Rich Proto-Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 339-339
Author(s):  
B.J. Hrivnak
Keyword(s):  
Optical Spectroscopy ◽  
Spectral Type ◽  
Planetary Nebulae ◽  
Luminosity Class ◽  
Dust Temperature ◽  
Medium Resolution

We are engaged in a program of optical spectroscopy of proto–planetary nebulae (PPN). The objects were initially selected from the IRAS database on the basis of their strong infrared excesses, indicating dust temperature of 150–250 K. Spectra have been obtrained at medium resolution for the purpose of obtaining the spectral type, luminosity class, and to search for chemical peculiarities resulting from the post–AGB nature of the objects. We found our PPN candidates to typically display F–G supergiant spectra.

scholarly journals Observed Relations Between Physical Properties and MK Classification as Functions of Metal Abundance for F5-K4 Stars

1976 ◽  
Vol 72 ◽  
pp. 75-78
Author(s):  
M. Grenon
Keyword(s):  
Physical Properties ◽  
Spectral Range ◽  
Spectral Type ◽  
Photometric System ◽  
Luminosity Class ◽  
Empirical Relations ◽  
Metal Abundance ◽  
Systematic Effects ◽  
The Absolute ◽  
Absolute Magnitudes

The Geneva photometric system has been calibrated in terms of [M/H], θeff, Mv in the spectral range F5 to K4. As the spectral type is a datum generally available, we derive empirical relations showing the coupling of θeff and [M/H] at given spectral type and luminosity class. Similar relations are offered for the absolute magnitudes and provide a more accurate means for deriving spectroscopic parallaxes. Systematic effects on the estimation of the luminosity class are also shown.

scholarly journals Hipparcos Positions of B/Be Stars on the HR Diagram

2000 ◽  
Vol 175 ◽  
pp. 117-128 ◽  
Author(s):  
Danielle Briot ◽  
Noel Robichon
Keyword(s):  
Spectral Type ◽  
Rotational Velocity ◽  
Absolute Magnitude ◽  
Be Stars ◽  
Class V ◽  
B Stars ◽  
Luminosity Class ◽  
The Mean ◽  
Absolute Magnitudes ◽  
Hipparcos Parallax

AbstractAbsolute magnitudes of Be and B stars are computed for each spectral type and luminosity class V and IV, using the Hipparcos parallax measurements. Some simulations have been carried out in order to estimate the effects which could bias the mean absolute magnitude calculations. As a result, only stars with σπ/π < 15% have been used. A first result is that B stars are fainter than previous estimations by about 0.5 magnitude on average. We then observe that on average Be stars are brighter than B stars of the same spectral type and this over-luminosity increases with the spectral type. A possible interpretation is proposed based on the fact that the rotational velocity of the late Be stars is near the critical rotational velocity.

Optical spectroscopy of Magellanic Cloud planetary nebulae.

1991 ◽  
Vol 75 ◽  
pp. 407 ◽  
Author(s):  
Stephen J. Meatheringham ◽  
Michael A. Dopita
Keyword(s):  
Optical Spectroscopy ◽  
Planetary Nebulae ◽  
Magellanic Cloud

Lithium in Cool Stars Detected in EUV Surveys

2000 ◽  
Vol 198 ◽  
pp. 366-367 ◽  
Author(s):  
G. Tagliaferri ◽  
L. Pastori ◽  
G. Cutispoto ◽  
R. Pallavicini
Keyword(s):  
Spectral Line ◽  
Spectral Type ◽  
Rotational Velocity ◽  
Luminosity Class ◽  
Photometric Observations ◽  
Cool Stars ◽  
Active Cool

We selected a sample of active cool stars detected in the EUV band by the ROSAT WFC and performed spectroscopic and photometric observations. We inferred spectral type, luminosity class, distance, binary status, rotational velocity. Here we show the results of the Li abundances determination from the Li I 6707.8 Å spectral line.

scholarly journals Precise calibration of the dependence of surface brightness–colour relations on colour and class for late-type stars

2020 ◽  
Vol 640 ◽  
pp. A2 ◽  
Author(s):  
A. Salsi ◽  
N. Nardetto ◽  
D. Mourard ◽  
O. Creevey ◽  
D. Huber ◽  
...  
Keyword(s):  
Spectral Type ◽  
Surface Brightness ◽  
Eclipsing Binaries ◽  
Angular Diameter ◽  
Late Type ◽  
Luminosity Class ◽  
Photometric Observations ◽  
Photometric Measurements ◽  
Selection Of

Context. Surface brightness–colour relations (SBCRs) are used to derive the stellar angular diameters from photometric observations. They have various astrophysical applications, such as the distance determination of eclipsing binaries or the determination of exoplanet parameters. However, strong discrepancies between the SBCRs still exist in the literature, in particular for early and late-type stars. Aims. We aim to calibrate new SBCRs as a function of the spectral type and the luminosity class of the stars. Our goal is also to apply homogeneous criteria to the selection of the reference stars and in view of compiling an exhaustive and up-to-date list of interferometric late-type targets. Methods. We implemented criteria to select measurements in the JMMC Measured Diameters Catalog. We then applied additional criteria on the photometric measurements used to build the SBCRs, together with stellar characteristics diagnostics. Results. We built SBCRs for F5/K7–II/III, F5/K7–IV/V, M–II/III and M–V stars, with respective rms of σFV = 0.0022 mag, σFV = 0.0044 mag, σFV = 0.0046 mag, and σFV = 0.0038 mag. This results in a precision on the angular diameter of 1.0%, 2.0%, 2.1%, and 1.7%, respectively. These relations cover a large V − K colour range of magnitude, from 1 to 7.5. Our work demonstrates that SBCRs are significantly dependent on the spectral type and the luminosity class of the star. Through a new set of interferometric measurements, we demonstrate the critical importance of the selection criteria proposed for the calibration of SBCR. Finally, using the Gaia photometry for our samples, we obtained (G − K) SBCRs with a precision on the angular diameter between 1.1% and 2.4%. Conclusions. By adopting a refined and homogeneous methodology, we show that the spectral type and the class of the star should be considered when applying an SBCR. This is particularly important in the context of PLATO.

scholarly journals Low-Level Stellar Variability

1993 ◽  
Vol 137 ◽  
pp. 693-707 ◽  
Author(s):  
M. Grenon
Keyword(s):  
Spectral Type ◽  
Effective Temperature ◽  
Light Curves ◽  
Luminosity Class ◽  
Low Level ◽  
Variability Level ◽  
Hr Diagram

AbstractThe capability of ground-based photometry to detect and monitor low-level stellar variations is discussed in the particular case of amplitudes in the range of few magnitudes to few percent. The technical and atmospherical constraints are briefly recalled. The variability level of the so-called constant stars is discussed as function of the spectral type, the luminosity class and the effective temperature. The photometric aspects of the Hipparcos mission are presented here since this satellite allows a systematic detection of microvariables and the obtention of light curves across the whole HR-diagram with an unprecedented efficiency.

scholarly journals Spectroscopy-What are The Needs Once Space Astrometry has Given us a New Data Base

1980 ◽  
Vol 5 ◽  
pp. 795-798
Author(s):  
C. Jaschek
Keyword(s):  
Quantitative Analysis ◽  
Data Base ◽  
Spectral Type ◽  
Luminosity Class ◽  
Spectroscopic Information ◽  
Space Astrometry

I think the best way to start my talk is to recall what kind of spectroscopic, information is available at present. Spectroscopic information can be of various kinds; starting from the simplest it may be:a- a spectral type (unidimensional)b- a spectral type plus a luminosity class (bi-dimensional type)c- a description-more or less detailedd- a quantitative analysis, which can be more or less sophisticated

scholarly journals UV-NIR spectra of two planetary nebulae with X-Shooter

2011 ◽  
Vol 7 (S283) ◽  
pp. 508-509
Author(s):  
Cezary Szyszka ◽  
Jeremy R. Walsh ◽  
Albert A. Zijlstra
Keyword(s):  
Wavelength Range ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Single Shot ◽  
Medium Resolution ◽  
The Many

AbstractThe ESO VLT spectrograph X-shooter is currently the only one capable of observing the range from 330 nm up to 2.5 μm in a single shot. X-shooter is very suitable for study of the many diagnostic emission lines in PN providing a uniform flux scale at medium resolution over a large instantaneous wavelength range. Spectroscopy of two contrasting PNe, NGC 6302 and M 2-9, were observed and methods explored for identification of the many fitted emission lines.

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