scholarly journals Applications of the UB1B2V1G Photometric System

1973 ◽  
Vol 50 ◽  
pp. 145-151
Author(s):  
M. Golay
Keyword(s):  
Absolute Magnitude ◽  
Interstellar Extinction ◽  
Stellar Atmospheres ◽  
Physical Parameters ◽  
Photometric System ◽  
Peculiar Stars ◽  
Valid Comparison ◽  
Effects Of Rotation ◽  
First Time

This photometric system which was described for the first time in 1963 by Golay has been in use at the Geneva Observatory since 1959. We are involved in a long term observational programme having as objective the study of cluster stars, peculiar stars and interstellar extinction. This research aims at the determination of physical parameters such as effective temperature, gravity, abundance, or those of spectral type, absolute magnitude, [Fe/H]. To permit such an analysis the photometric effects of rotation, of multiplicity and of interstellar extinction were given particular attention. Attempting to attain the above mentioned purposes, we have had to give great care to the precision of the measurements during their acquisition as also during their reduction. Finally, in view of allowing a valid comparison between observations and the theory of stellar atmospheres, particular care had to be given to the maintenance of the pass-bands and to the knowledge of their form.We intend here to give the main bibliographical references relative to the articles which present the general properties of the system, its applications and the catalogues.

scholarly journals The Galactic WC and WO stars

2019 ◽  
Vol 621 ◽  
pp. A92 ◽  
Author(s):  
A. A. C. Sander ◽  
W.-R. Hamann ◽  
H. Todt ◽  
R. Hainich ◽  
T. Shenar ◽  
...  
Keyword(s):  
Mass Loss ◽  
Gamma Ray ◽  
Absolute Magnitude ◽  
Mass Range ◽  
Massive Black Holes ◽  
Open Questions ◽  
Late Evolution ◽  
First Time ◽  
Radius Problem

Wolf-Rayet stars of the carbon sequence (WC stars) are an important cornerstone in the late evolution of massive stars before their core collapse. As core-helium burning, hydrogen-free objects with huge mass-loss, they are likely the last observable stage before collapse and thus promising progenitor candidates for type Ib/c supernovae. Their strong mass-loss furthermore provides challenges and constraints to the theory of radiatively driven winds. Thus, the determination of the WC star parameters is of major importance for several astrophysical fields. With Gaia DR2, for the first time parallaxes for a large sample of Galactic WC stars are available, removing major uncertainties inherent to earlier studies. In this work, we re-examine a previously studied sample of WC stars to derive key properties of the Galactic WC population. All quantities depending on the distance are updated, while the underlying spectral analyzes remain untouched. Contrasting earlier assumptions, our study yields that WC stars of the same subtype can significantly vary in absolute magnitude. With Gaia DR2, the picture of the Galactic WC population becomes more complex: We obtain luminosities ranging from logL/L⊙ = 4.9–6.0 with one outlier (WR 119) having logL/L⊙ = 4.7. This indicates that the WC stars are likely formed from a broader initial mass range than previously assumed. We obtain mass-loss rates ranging between log Ṁ = −5.1 and −4.1, with Ṁ ∝ L0.68 and a linear scaling of the modified wind momentum with luminosity. We discuss the implications for stellar evolution, including unsolved issues regarding the need of envelope inflation to address the WR radius problem, and the open questions in regard to the connection of WR stars with Gamma-ray bursts. WC and WO stars are progenitors of massive black holes, collapsing either silently or in a supernova that most-likely has to be preceded by a WO stage.

scholarly journals Possible substellar companions in low-mass eclipsing binaries: GU Bootis and YY Geminorum

2018 ◽  
Vol 620 ◽  
pp. A72
Author(s):  
M. Wolf ◽  
H. Kučáková ◽  
P. Zasche ◽  
J. Vraštil ◽  
K. Hoňková ◽  
...  
Keyword(s):  
Precise Determination ◽  
Time Effect ◽  
Eclipsing Binaries ◽  
Physical Parameters ◽  
The Third ◽  
Low Mass ◽  
Orbital Periods ◽  
First Time

We present the next results of our long-term observational project to analyze the variations in the orbital periods of low-mass eclipsing binaries. About 70 new precise mid-eclipse times recorded with a CCD were obtained for two eclipsing binaries with short orbital periods: GU Boo (P = 0.​d49) and YY Gem (0.​d81). Observed-minus-calculated diagrams of the stars were analyzed using all reliable timings, and new parameters of the light-time effect were obtained. We derived for the first time or improved the short orbital periods of possible third bodies of 11 and 54 years for these low-mass binaries, respectively. We calculated that the minimum masses of the third components are close to 50 MJup, which corresponds to the mass of brown dwarfs. The multiplicity of these systems also plays an important role in the precise determination of their physical parameters.

scholarly journals Absolute Magnitude Determination of Be Stars: The Inadequacy of the 2200 Å Bump

1993 ◽  
Vol 137 ◽  
pp. 787-788 ◽  
Author(s):  
V. Doazan ◽  
A. De La Fuente ◽  
M. Barylak ◽  
N. Cramer
Keyword(s):  
Absolute Magnitude ◽  
Interstellar Extinction ◽  
Be Stars ◽  
Distance Determination ◽  
Type Spectrum ◽  
Magnitude Determination

AbstractWe present fax UV observations of Pleione made with the IUE satellite at two epochs: in 1979, when the star exhibited a strong shell spectrum and, in 1991, when it showed a Be-type spectrum. Between these two epochs, the 2200 Å bump changed dramatically, thus, rendering it inadequate for interstellar extinction/distance determination.

New calibration of the Vilnius photometric system

2018 ◽  
Vol 14 (A30) ◽  
pp. 486-486
Author(s):  
M. Maskoliunas ◽  
J. Zdanavičius ◽  
V. Čepas ◽  
A. Kazlauskas ◽  
R. P. Boyle ◽  
...  
Keyword(s):  
Photometric Determination ◽  
High Dispersion ◽  
Physical Parameters ◽  
Photometric System ◽  
Homogeneous Sample ◽  
Giant Stars ◽  
Stellar Temperatures ◽  
Absolute Magnitudes ◽  
Gaia Dr2

AbstractThe medium-band Vilnius photometric system with the mean wavelengths at 345 (U), 374 (P), 405 (X), 466 (Y), 516 (Z), 544 (V), and 656 (S) nm for many years was an important tool to determine interstellar reddenings and distances of single stars due to its ability to classify stars of all temperatures in spectral classes and luminosity classes in the presence of different interstellar reddenings. At present, Gaia DR2 presents distances to stars with an unprecedented accuracy at least up to 3 kpc. However, multicolor photometry, which allows the classification of stars as well as the preliminary determination of stellar temperatures, gravities, metallicities and interstellar reddenings, remains an important method for distant stars. Here we present an empirical calibration of the intrinsic color indices of the Vilnius system in terms of physical parameters of stars for dwarf and giant stars of spectral classes F-G-K-M. In any attempted photometric determination of physical parameters of stars it is important to have an extensive and homogeneous sample of spectroscopically determined parameters for stars for which there are also accurate photometric data. As a source catalogue for the Vilnius photometry the latest updated version of the Catalogue of Photoelectric Observations in the Vilnius System was used, which contains compilations from the published photometry for about 11 000 stars. The stars which had both the Gaia DR2 parallaxes and the determinations of stellar parameters from high-dispersion spectra were extracted from this catalogue. The final sample contains more than 1500 stars of spectral classes F-M. The majority of these stars (ca 70%) are not reddened, for others the values of interstellar reddening AV were determined using the regular techniques of photometric classification in the Vilnius system. The absolute magnitudes MV and consequently the luminosity classes were determined using Gaia DR2 parallaxes. We present the analytical expressions for the effective temperature Teff and surface gravity logg and evaluate the errors of solutions for dwarf and giant stars. To test the accuracy of the proposed method, we have compared our results with the stars observed by Gaia and with the stellar parameters available from the large spectroscopic surveys: APOGEE, Gaia-ESO, GALAH, LAMOST, RAVE and SEGUE. The results of comparison contain 5-6 % outliers.The proposed method allows the fast and straightforward evaluation of stellar physical parameters for the stars observed in the Vilnius photometric system. Despite the fact, that the accuracy of determination is significantly lower than in the case of spectroscopic methods, the method described may be useful for distant faint stars, which are still inaccessible for spectroscopic observations.

scholarly journals CCD Photometry of the M 67 Cluster in the Vilnius Photometric System

1995 ◽  
Vol 167 ◽  
pp. 363-364
Author(s):  
R. Boyle ◽  
V. Straižys ◽  
F. Vrba ◽  
F. Smriglio ◽  
A. K. Dasgupta
Keyword(s):  
High Sensitivity ◽  
Physical Parameters ◽  
Spectroscopic Methods ◽  
Wide Field ◽  
Photometric System ◽  
Ccd Photometry ◽  
Absolute Magnitudes ◽  
Ccd Detectors

The Vilnius photometric system, consisting of seven passbands at 345, 374, 405, 466, 516, 544 and 656 nm makes it possible to determine spectral classes (or temperatures), absolute magnitudes (or surface gravities), metallicities and peculiarity types for stars of all spectral types in the presence of interstellar reddening (Straizys 1977, 1992a, b). This makes the system very useful for the determination of the physical parameters of stars which are too faint to be studied by spectroscopic methods. The system is especially effective when used with CCD detectors which combine a wide field, high sensitivity and high photometric accuracy.

scholarly journals The Luminosity Calibration of the uvby — β Photometry

2002 ◽  
Vol 12 ◽  
pp. 684-687 ◽  
Author(s):  
C. Jordi ◽  
X. Luri ◽  
E. Masana ◽  
J. Torra ◽  
F. Figueras ◽  
...  
Keyword(s):  
Rotational Velocity ◽  
Statistical Treatment ◽  
Zero Point ◽  
Absolute Magnitude ◽  
Physical Parameters ◽  
Photometric System ◽  
Intermediate Band ◽  
System A ◽  
Small Zero

AbstractThe ESA HIPPARCOS satellite has provided astrometry of unprecedented accuracy, allowing us to reassess, improve and refine the pre-Hipparcos luminosity calibrations. We review the “classical” absolute magnitude calibrations with the Strömgren-Crawford intermediate-band photometric system. A small zero point correction of about 2-4% seems necessary, as well as to refine the dependences on metallicity and projected rotational velocity. The need of a rigorous statistical treatment of the extremely precise Hipparcos data to derive definitive dependences of the luminosity on physical parameters is emphasized.

Disability as a social phenomenon

2020 ◽  
pp. 22-38
Author(s):  
Natalia Guseva ◽  
Vitaliy Berdutin
Keyword(s):  
Social Protection ◽  
Russian Society ◽  
Stage Model ◽  
High Quality ◽  
Rehabilitation Programs ◽  
Current State ◽  
The Social ◽  
Consistent Solution ◽  
First Time

At present, the problem of establishing disability is a point at issue in Russia. Despite the fact that medical criteria for disability are being developed very actively, high-quality methods for assessing social hallmarks are still lacking. Since disability is a phenomenon inherent in any society, each state forms a social and economic policy for people with disabilities in accordance with its level of development, priorities and opportunities. We have proposed a three-stage model, which includes a system for the consistent solution of the main tasks aimed at studying the causes and consequences of the problems encountered today in the social protection of citizens with health problems. The article shows why the existing approaches to the determination of disability and rehabilitation programs do not correspond to the current state of Russian society and why a decrease in the rate of persons recognized as disabled for the first time does not indicate an improvement in the health of the population. The authors proposed a number of measures with a view to correcting the situation according to the results of the study.

Phytochemical Constituents of Annona reticulata and their Cytotoxic Activity

2020 ◽  
Vol 17 (3) ◽  
pp. 206-210
Author(s):  
Ty Viet Pham ◽  
Thang Quoc Le ◽  
Anh Tuan Le ◽  
Hung Quoc Vo ◽  
Duc Viet Ho
Keyword(s):  
Cytotoxic Activity ◽  
Cell Lines ◽  
Structural Determination ◽  
Phytochemical Investigation ◽  
Ic50 Values ◽  
Phytochemical Constituents ◽  
First Time ◽  
Annona Reticulata

A phytochemical investigation of the leaves of Annona reticulata led to the isolation and structural determination of β-sitosterol (1), ent-pimara-8(14),15-dien-19-oic acid (2), ent-pimara- 8(14),15-dien-19-ol (3), quercetin (4), quercetin 3-O-α-L-arabinopyranoside (5), and a mixture of quercetin 3-O-β-D-galactopyranoside (6a) and quercetin 3-O-β-D-glucopyranoside (6b). Of these, compounds 2 and 3 were isolated from the genus Annona for the first time. Compound 3 showed strong cytotoxicity against SK-LU-1 and SW626 cell lines with IC50 values of 17.64 ± 1.07 and 19.79 ± 1.41 μg mL-1, respectively.

Development of an HPLC-UV Method for Quantification of Stattic

2019 ◽  
Vol 15 (6) ◽  
pp. 568-573
Author(s):  
Soheil Sedaghat ◽  
Ommoleila Molavi ◽  
Akram Faridi ◽  
Ali Shayanfar ◽  
Mohammad Reza Rashidi
Keyword(s):  
High Performance ◽  
Accurate Method ◽  
Plasma Samples ◽  
Promising Target ◽  
Relative Standard ◽  
Dimerization Inhibitor ◽  
Oncogenic Protein ◽  
First Time ◽  
Transcription 3

Background: Signal transducer and activator of transcription 3 (STAT3), an oncogenic protein found constitutively active in many types of human malignancies, is considered to be a promising target for cancer therapy. Objective: In this study for the first time, a simple and accurate method has been developed for the determination of a STAT3 dimerization inhibitor called stattic in aqueous and plasma samples. Methods: A reverse-phase high-performance liquid chromatography (RP-HPLC) composed of C18 column as stationary phase, and the mixture of acetonitrile (60%) and water (40%) as mobile phase with a UV detection at 215 nm were applied for quantification of stattic. The developed method was validated by Food and Drug Administration (FDA) guideline. Results: The method provided a linear range between 1-40 and 2.5-40 µg mL-1 for aqueous and plasma samples, respectively, with a correlation coefficient of 0.999. The accuracy (as recovery) of the developed method was found to be between 95-105% for aqueous medium and 85-115% for plasma samples. The precision (as relative standard deviation) for aqueous and plasma samples was less than 6% and 15%, respectively. The sensitivity of the developed method based on FDA guideline was 1 µg mL-1 for aqueous and 2.5 µg mL-1 for plasma samples. Conclusion: These results show that the established method is a fast and accurate quantification for stattic in aqueous and plasma samples.

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