scholarly journals The Absolute Calibration of the HR Diagram: Fundamental Effective Temperatures and Bolometric Corrections

1978 ◽  
Vol 80 ◽  
pp. 65-76 ◽  
Author(s):  
D. S. Hayes
Keyword(s):  
Spectral Type ◽  
Absolute Calibration ◽  
Effective Temperatures ◽  
The Absolute ◽  
Hr Diagram

Scales of fundamental bolometric connections (B.C.) and effective temperatures (Teff) as a function of spectral type or color are necessary for the comparison of observations and theory in the HR diagram.

A discussion on infared astronomy - Near infrared photometry of late-type stars

1969 ◽  
Vol 264 (1150) ◽  
pp. 209-225 ◽  
Keyword(s):  
Spectral Type ◽  
Near Infrared ◽  
Model Atmosphere ◽  
Spectral Irradiance ◽  
Photometric Method ◽  
Infrared Photometry ◽  
Late Type ◽  
Stellar Diameters ◽  
Effective Temperatures ◽  
The Absolute

A multi-band photoelectric photometer for observations in the ultraviolet, blue and visible and the infrared bands W (1.06μm), X (1.13 μm, Y (1.63 μm) and Z (2.21 μm) has been constructed and applied to both stellar and planetary observations. The results of photometry obtained for 61 stars are presented. The observations at λ = 1.63 μm are shown to exhibit an excess flux due to a minimum in the H opacity in accordance with the predictions of model atmosphere studies. Bolometric corrections are derived for stars of late spectral type from integration of the observed absolute spectral irradiance curve. A simple photometric method for the measurement of stellar diameters is proposed based upon the absolute irradiance observed at 2.21 μm and the 2.21 μm flux at the surface of the star calculated from model atmospheres. Angular diameters derived by this technique are consistent with interferometric results; and, when combined with the bolometric corrections, effective temperatures are found.

scholarly journals The Position of the Sun in the HR Diagram

1978 ◽  
Vol 80 ◽  
pp. 89-90
Author(s):  
Don C. Barry
Keyword(s):  
Quantitative Analysis ◽  
Spectral Line ◽  
Spectral Type ◽  
Main Sequence ◽  
Solar Spectrum ◽  
Absolute Magnitude ◽  
Systematic Difference ◽  
The Sun ◽  
The Absolute ◽  
Hr Diagram

Since the absolute magnitude of the Sun is known accurately and the solar spectrumdefinesspectral type G2 V, it would appear that the position of the Sun in the HR diagram is well established. However, the color of the Sun and its metallicity relative to other stars remains controversial. It is known from theory that stellar groups of differing composition will have different main sequences.The observed difference in the strength of the metallic lines in Coma stars relative to Hyades stars is caused by a systematic difference in [Fe/H] of less than 0.2 dex or 50%. Photographs and quantitative measures of the systematic differences between the Hyades and Coma spectra are presented. Visual comparison and quantitative analysis of the solar spectrum relative to Hyades and Coma spectra reveal that the Sun is metal rich similar to the Hyades stars rather than of normal disk metallicity as represented by Coma stars. Evidence is presented showing that the color and spectral line strengths of the Sun are more similar to stars classified G3 and G4 in the literature than G2. If the Hyades modulus is y = 3m.25, the (B-V) color of the Sun must be 0m.65 or redder for the Sun to be on or above the Hyades main sequence.

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 Sakurai’s Object: Constraints from its Variability?

1998 ◽  
Vol 11 (1) ◽  
pp. 360-360
Author(s):  
T. Gautschy ◽  
H.W. Duerbeck ◽  
A.M. Van Genderen ◽  
S. Benetti
Keyword(s):  
Cooling Rate ◽  
Nuclear Energy ◽  
Stability Analyses ◽  
The Past ◽  
Stellar Pulsations ◽  
First Results ◽  
Effective Temperatures ◽  
Stellar Envelopes ◽  
Light Variability ◽  
Hr Diagram

The peculiar outburst of the star baptized Sakurai’s Object (SO) is a conceivable example of a late He shell flash in a post-AGB object. The new source of nuclear energy forces such objects toward high luminosities and eventually low effective temperatures; they cross the HR diagram in a comparable fashion as FG Sge did in the past - i.e., they move noticeably on the HR diagram on human timescales. From monitoring campaigns of SO during the last year, first estimates of its cooling rate were derived and in particular cyclic light variability was established. We present first results from attempts to model stellar envelopes appropriate for SO. As we hypothesize the light variability to be attributable to stellar pulsations, we aim at constraining the basic stellar parameters based on stability analyses of our envelope models. Radial, nonadiabatic stability computations provided predictions of the modal content which should be observable as SO evolves. The particular components in such mode spectra of SO as they are to appear in the coming years should indeed help to constrain basic stellar parameters such as mass and luminosity.

Electron–photon coincidence technique for the absolute calibration of VUV detectors

1983 ◽  
Vol 22 (10) ◽  
pp. 1551 ◽  
Author(s):  
R. McAdams ◽  
S. K. Srivastava
Keyword(s):  
Absolute Calibration ◽  
Coincidence Technique ◽  
The Absolute ◽  
Electron Photon

scholarly journals Absolute Calibration or Validation of the Altimeters on the Sentinel-3A and the Jason-3 over Lake Issykkul (Kyrgyzstan)

2018 ◽  
Vol 10 (11) ◽  
pp. 1679 ◽  
Author(s):  
Jean-François Crétaux ◽  
Muriel Bergé-Nguyen ◽  
Stephane Calmant ◽  
Nurzat Jamangulova ◽  
Rysbek Satylkanov ◽  
...  
Keyword(s):  
Satellite System ◽  
Reference Points ◽  
Absolute Calibration ◽  
In Situ Data ◽  
Absolute Bias ◽  
Weather Stations ◽  
Field Campaigns ◽  
The Absolute ◽  
Gps System ◽  
Water Height

Calibration/Validation (C/V) studies using sites in the oceans have a long history and protocols are well established. Over lakes, C/V allows addressing problems such as the performance of the various retracking algorithms and evaluating the accuracy of the geophysical corrections for continental waters. This is achievable when measurements of specific and numerous field campaigns and a ground permanent network of level gauges and weather stations are processed. C/V consists of installation of permanent sites (weather stations, limnigraphs, and GPS reference points) and the organization of regular field campaigns. The lake Issykkul serves as permanent site of C/V, for a multi-mission purpose. The objective of this paper is to calculate the altimeter biases of Jason-3 and Sentinel-3A, both belonging to an operational satellite system which is used for the long-term monitoring of lake level variations. We have also determined the accuracy of the altimeters of these two satellites, through a comparison analysis with in situ data. In 2016 and 2017, three campaigns have been organized over this lake in order to estimate the absolute bias of the nadir altimeter onboard the Jason-3 and Sentinel-3A. The fieldwork consisted of measuring water height using a GPS system, carried on a boat, along the track of the altimeter satellite across the lake. It was performed at the time of the pass of the altimeter. Absolute altimeter biases were calculated by averaging the water height differences along the pass of the satellite (GPS from the boat system versus altimetry). Jason-3 operates in a Low Resolution Mode (LRM), while the Sentinel-3A operates in Synthetic Aperture Radar (SAR) mode. In this study we found that the absolute biases measured for Jason-3 were −28 ± 40 mm with the Ocean retracker and 206 ± 30 mm with the Ice-1 retracker. The biases for Sentinel-3A were −14 ± 20 mm with the Samosa (Ocean like) retracker and 285 ± 20 mm with the OCOG (Ice-1-like) retracker. We have also evaluated the accuracy of these two altimeters over Lake Issykkul which reached to 3 cm, for both the instruments, using the Ocean retracker.

scholarly journals The Status of the Absolute Calibration of Stellar Fluxes Between 912 and 1200 Å

1985 ◽  
Vol 111 ◽  
pp. 479-483
Author(s):  
R. S. Polidan ◽  
J. B. Holberg
Keyword(s):  
Planetary Nebula ◽  
White Dwarfs ◽  
Main Sequence ◽  
Absolute Calibration ◽  
Energy Distributions ◽  
B Stars ◽  
The Status ◽  
The Absolute ◽  
Flux Calibration

Recent results have shed new light on the status of the calibration of absolute stellar fluxes between 912 and 1200 Å. Observations of hot white dwarfs, subdwarfs and planetary nebula nuclei with the Voyager ultraviolet spectrometers provide evidence that the current calibration agrees very well with extrapolations of IUE energy distributions shortwards of 1200 Å. Voyager observations of main sequence B-stars used as flux calibration sources have revealed that many are variable in brightness in the 912–1200 Å region. We conclude there is no current observational motivation for any revision of the 912 to 1200 Å calibration described by Holberg et al. (1982).

scholarly journals Method for the Absolute Calibration of Direct-Current Current Transducers

2019 ◽  
Vol 68 (6) ◽  
pp. 1961-1966 ◽  
Author(s):  
Jianting Zhao ◽  
Yunfeng Lu ◽  
Changwei Zhai ◽  
Qing He ◽  
Xiaoding Huang ◽  
...  
Keyword(s):  
Direct Current ◽  
Absolute Calibration ◽  
The Absolute
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