共查询到20条相似文献，搜索用时 46 毫秒
1.
We present here, for the O and B type stars in the Catalogue of Stellar Ultraviolet Fluxes, an approach which does not require
a precise knowledge of spectral type and luminosity class for derivingE(B-V) colour excesses. The method is based on the use of an UV-visual two-colour diagram; galactic variations in the interstellar
extinction law are analyzed and fully taken into account. Our results have been compared with those derived by using the differences
between observed and intrinsic colours for stars with known spectral classification. The very good agreement in a large number
of cases (94 per cent) demonstrates that our approach permits the derivation of reliable colour excess values for early type
stars even if only a rough spectral classification is available. 相似文献
2.
An analysis of the stars included in the catalogue of λ Bootis by Paunzen et al. (1997) and with IUE Low Resolution observations
is presented here. Using line-ratios of carbon to heavier elements (Al and Ni) allows us to establish unambiguous membership
criteria for the λ Bootis group. These criteria have been used to look for new λ Bootis candidates in the IUE Final Archive.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
L. A. Yakovina Ya. V. Pavlenko K. Abia A. E. Rozenbush 《Kinematics and Physics of Celestial Bodies》2011,27(5):233-248
We determine lithium abundances in atmospheres of three carbon stars from synthetic spectrum fitting in the λλ 668–674 nm
range using the Li I λ 670.8 nm resonance doublet. To produce synthetic spectra, we use a modified list of atomic lines from
the VALD database and three alternative line lists of CN and C2 molecules which are modifications of line lists from the Jorgensen’s website () and from the Kurucz database (1993, CD-ROM nos. 1–23). The spectral lines from these lists were tested by matching synthetic
spectra to observed spectra of the sun, Arcturus, and early R star HD 100764. We perform analysis of the blends involving
the Li I λ 670.8 nm doublet in spectra of N stars AW Cyg and UX Dra. The lithium abundances in HD 100764, AW Cyg, and UX Dra
are estimated to be lgN(Li) ≈ 2, −1.4, and −0.9, respectively. Discrepancies of lithium abundances lgN(Li) obtained with the help of molecular line lists do not seem to exceed 0.2 dex. 相似文献
4.
N. G. Mykhailytska 《Kinematics and Physics of Celestial Bodies》2010,26(6):302-312
In the spectral region λλ = 610.25−610.57 nm of the roAp star HD 101065, we performed the identification of the rare-earth
element absorption lines absent from the atomic spectral line databases VALD and DREAM. The identified lines were used for
calculating the synthetic spectra of the roAp stars HD 137949, HD 134214, and HD 24712. The upper limit of the identified
line estimates was determined. The rotation/pulsation parameter νsini and magnetic field modulus were determined using the lines Nd III 669.083 nm and Ca I 616.217 nm. The element abundance in
the roAp stars HD 134214 and HD 24712 was determined for the first time using Nd III lines. Calculations were carried out
with the help of the code SynthM developed by S.A. Khan. 相似文献
5.
The populations of B and Be-stars in the young open clusters NGC 7419 and NGC 659 are studied. Lowresolution spectral observations
in the region of the Hα line are used to study 34 members of NGC 7419 and additional spectra in the range λ3700-6200 ? are
obtained for 12 stars. During the period of our observations, four previously identified Be-stars manifested an absorption
profile for the Hα line. Emission in the Hα line is observed in the spectra of 21 objects. The members of the cluster NGC
7419 are classified as to spectral type. The position of the Be-stars on a two-color IR diagram and a comparison with the
position of the objects in other clusters with similar ages cast doubt on the existence of two starformation waves. Moderate
resolution spectra were obtained for 22 stars in the cluster NGC 659 over wavelengths of λ4050-5200 ? and for 7 objects in
the neighborhood of the Hα line. Emission is observed in both the Hα and Hβ lines for two of the five Be-stars that were studied,
while faint emission appears only in the Hα line in one of the stars. The other members of the cluster show no signs of emission
in these spectra. Teff, log g, and Vsini are estimated for the observed stars. It is found that 5 of the objects are not members of the cluster. 相似文献
6.
The results of the spectral classification of newly discovered M-type variables obtained as part of an H-alpha survey of Galactic dark cloud regions are presented. The survey was carried out with the 40 Schmidt camera of Byurakan Observatory, and the spectra of the variable stars for the classification were obtained with the Observatory's 2.6-m telescope. The observational material allowed register of late M-type variables as well as their brightness variations. Among the 97 newly discovered M-type stars, 22 show brightness variations. The results of the spectral classification of these new variables show that 21 out of 22 are red giants, and in all probability they are Mira Ceti type long period variables. 相似文献
7.
We employ an Artificial Neural Network (ANN) based technique to develop a pipeline for automated segregation of stars from the galaxies to be observed by Tel-Aviv University Ultra-Violet Experiment (TAUVEX). We use synthetic spectra of stars from UVBLUE library and selected International Ultraviolet Explorer (IUE) low-resolution spectra for galaxies in the ultraviolet (UV) region from 1250 to 3220 Å as the training set and IUE low-resolution spectra for both the stars and the galaxies as the test set. All the data sets have been pre-processed to get band integrated fluxes so as to mimic the observations of the TAUVEX UV imager. We also perform the ANN based segregation scheme using the full length spectral features (which will also be useful for the ASTROSAT mission). Our results suggest that, in the case of the non-availability of full spectral features, the limited band integrated features can be used to segregate the two classes of objects; although the band data classification is less accurate than the full spectral data classification. 相似文献
8.
We present moderate resolution CCD spectra and R photometry for seven KP2001 stars. We revised the spectral classification of the stars in the range λλ4000−8700? . Our photometric
data confirmed the behavior of the light curves downloaded from the NSVS (Northern Sky Variability Survey) database. For KP2001-32,
presented as a Mira-type variable in NSVS, we estimated absolute bolometric M
b and K-band M
K
magnitudes as well as the distance using the period-luminosity relations. We also estimated the mass loss rate using the
calibration relations between mass loss rate and K - [12] index. From the position in infrared color-color diagrams, we confirmed the photometric classification of KP2001-221
as a semiregular variable, based on the light curve of the NSVS database. For the N-type carbon star KP2001-77 we estimated
distance and absolute magnitude M
K
using different calibration methods. For the remaining four objects we derived the absolute magnitudes and distances using
our CCD spectra and published JHK
S
magnitudes. We discuss the nature of these objects on the basis of the obtained results. 相似文献
9.
A. S. Shugarov N. V. Chupina A. E. Piskunov N. V. Kharchenko 《Astrophysics and Space Science》2011,335(1):317-321
Precise pointing and stabilization of the T-170M telescope (World Space Observatory Ultraviolet, WSO-UV project) is provided
by the Fine Guidance System (FGS) that uses a guide star catalogue (Master Catalogue). To verify the photometric system of
the Master Catalogue we have carried out ground based observations with a CCD-camera in a spectral band, close to that of
FGS. We have found, that the photometric quality of the Master Catalogue is sufficient for FGS operations. The mean photometric
error in the range of 14–17 mag is ±0.23 mag; its variation over the sky does not exceed the factor of two. 2% of stars from
the Master Catalogue have photometric errors higher than 2 mag. We have also found a correlation between large photometric
errors and the Master Catalogue flags. 相似文献
10.
The Solar–Stellar Irradiance Comparison Experiment {II (SOLSTICE {II), aboard the Solar Radiation and Climate Experiment (SORCE)
spacecraft, consists of a pair of identical scanning grating monochromators, which have the capability to observe both solar
spectral irradiance and stellar spectral irradiance using a single optical system. The SOLSTICE science objectives are to
measure solar spectral irradiance from 115 to 320 nm with a spectral resolution of 1 nm, a cadence of 6 h, and an accuracy
of 5%, to determine its variability with a long-term relative accuracy of 0.5% per year during a 5-year nominal mission, and
to determine the ratio of solar irradiance to that of an ensemble of bright B and A stars to an accuracy of 2%. Those objectives
are met by calibrating instrument radiometric sensitivity before launch using the Synchrotron Ultraviolet Radiation Facility
at the National Institute for Standards and Technology in Gaithersburg, Maryland. During orbital operations irradiance measurements
from an ensemble of bright, stable, main-sequence B and A stars are used to track instrument sensitivity. SORCE was launched
on 25 January 2003. After spacecraft and instrument check out, SOLSTICE {II first observed a series of three stars to establish
an on-orbit performance baseline. Since 6 March 2003, both instruments have been making daily measurements of both the Sun
and stars. This paper describes the pre-flight and in-flight calibration and characterization measurements that are required
to achieve the SOLSTICE science objectives and compares early SOLSTICE{II measurements of both solar and stellar irradiance
with those obtained by SOLSTICE {I on the Upper Atmosphere Research Satellite. 相似文献
11.
Astrometric CCD observations of 1123 stars with large proper motions (μ > 300 mas yr−1) from the LSPM (I/298) catalog in the declination zone +30°–+70° have been carried out with the Pulkovo normal astrograph
since 2006. The observational program includes mostly stars that previously have not entered into high-accuracy projects to
determine the proper motions. Our studies are aimed at determining new proper motions of fast stars in the HCRF/UCAC3 system
and searching for stars with invisible companions in the immediate Galactic neighborhoods of the Sun. Having analyzed about
10 000 CCD frames, we have obtained the equatorial coordinates of 414 program stars in the HCRF/UCAC3 system at an accuracy
level of 10–50 mas and determined their new proper motions. To derive the proper motions, we have used the data from several
star catalogs and surveys (M2000, CMC14, 2MASS, SDSS) as early epochs. The epoch differences range from 5 to 13 years (on
average, about 10 years); the mean accuracy of the derived proper motions is 4–5 mas yr−1. For 70 stars, we have revealed significant differences between the derived proper motions and those from the LSPM and I/306A
catalogs (these proper motions characterize the mean motion of the photocenter in 50 years or more). Apart from systematic
errors, these differences can result from the existence of invisible components of the program stars. 相似文献
12.
We present two new luminous blue variable (LBV) candidate stars discovered in the M33 galaxy. We identified these stars as
massive star candidates at the final stages of evolution, presumably with a notable interstellar extinction. The candidates
were selected from the Massey et al. catalog based on the following criteria: emission in H
α
, V<18./m 5 and 0.m 35 < (B - V) < 1.m 2. The spectra of both stars reveal a broad and strong H
α
emission with extended wings (770 and 1000 kms−1). Based on the spectra we estimated the main parameters of the stars. Object N45901 has a bolometric luminosity log(L/L⊙) = 6.0–6.2 with the value of interstellar extinction A
V
= 2.3 ± 0.1. The temperature of the star’s photosphere is estimated as T⋆ ∼ 13000–15000 K, its probable mass on the Zero
Age Main Sequence is M∼ 60–80 M⊙. The infrared excess in N 45901 corresponds to the emission of warm dust with the temperature Twarm ∼ 1000 K, and amounts
to 0.1%of the bolometric luminosity. A comparison of stellar magnitude estimates from different catalogs points to the probable
variability of the object N45901. Bolometric luminosity of the second object, N125093, is log(L/L⊙) = 6.3 − 6.6, the value of interstellar extinction is A
V
= 2.75 ± 0.15. We estimate its photosphere’s temperature as T⋆∼ 13000–16000K, the initial mass as M ∼ 90–120 M⊙. The infrared excess in N125093 amounts to 5–6% of the bolometric luminosity. Its spectral energy distribution reveals two
thermal components with the temperatures Twarm ∼ 1000K and Tcold ∼ 480 K. The [Ca II] λλ7291, 7323 lines, observed in LBV-like stars Var A and N93351 in M33 are also present in the spectrum of N 125093. These lines
indicate relatively recent gas eruptions and dust activity linked with them. High bolometric luminosity of these stars and
broad H
α emissions allow classifying the studied objects as LBV candidates. 相似文献
13.
We compare high-resolution spectra from the Sun and the four solar-type stars 16 Cyg A, 16 Cyg B, HD 32008, HD 34411 obtained with IUE in the wavelength range 2650–2930 Å. The comparison is made for peak intensities between absorption lines. At the level of accuracy of the IUE observations, the stars 16 Cyg A, 16 Cyg B, HD 34411 are indistinguishable from the Sun, in particular the Mgii resonance line profiles are identical. HD 32008 is not a solar analog but is evidently of late G to early K spectral type.Based on observations with the International Ultraviolet Explorer collected at the Villafranca Satellite Tracking Station of the European Space Agency. 相似文献
14.
《天文和天体物理学研究(英文版)》2015,(8)
In this work, we select spectra of stars with high signal-to-noise ratio from LAMOST data and map their MK classes to the spectral features. The equivalent widths of prominent spectral lines, which play a similar role as multi-color photometry, form a clean stellar locus well ordered by MK classes. The advantage of the stellar locus in line indices is that it gives a natural and continuous classification of stars consistent with either broadly used MK classes or stellar astrophysical parameters. We also employ an SVM-based classification algorithm to assign MK classes to LAMOST stellar spectra. We find that the completenesses of the classifications are up to 90% for A and G type stars, but they are down to about 50% for OB and K type stars. About 40% of the OB and K type stars are mis-classified as A and G type stars,respectively. This is likely due to the difference in the spectral features between late B type and early A type stars or between late G and early K type stars being very weak. The relatively poor performance of the automatic MK classification with SVM suggests that the direct use of line indices to classify stars is likely a more preferable choice. 相似文献
15.
The catalog of the classical WR stars which have the emission doublet Ovi 3811, 3834 in their optical spectra (the catalog of the WR-Ovi stars) and the results of the spectroscopic investigations of the WR-Ovi stars HD 16523, HD 17638, and HD 192103 are presented. Rapid spectral variability of the emission doublet Ovi 3811, 3834 in the spectra of WR-Ovi stars HD 16523, HD 17638, and of the emission band 3680-3780 Å in the spectra of the WR-Ovi star HD 16523 is observed. It is shown that spectral sub-types of the stars HD 16523 and HD 17638 as estimated from different criteria are uncertain. We argue that the WR-Ovi stars HD 16523 and HD 17638, the optical spectra of which display emission doublet Ovi 3811, 3834, may be considered as WO5 stars. The sub-type WO5 is proposed for the first time. Classification criteria of the WO5 sub-type are represented. The possible contribution of the ions Heii to the emission at 3811 Å and 3834 Å is investigated. Thez-distributions of WR-Ovi stars and WR stars with the probable relativistic companions are found to be similar. 相似文献
16.
Described here is a preliminary and tentative application of a method for fine-classification of stars, selected for studies
of galactic structure. The present investigation is based on about 100 stars within the approximate spectral type range B6-A5,
for which both spectra andUBV photometry have been obtained.
The motivation of the project is the following: For the study of galactic fine-structure it is essential to use as many members
as possible of stellar agglomerations of various type for a statistical treatment of the material. A-type stars are fairly
numerous and reasonably bright, but if all chemically peculiar stars, fast rotators or multiple systems have to be omitted
there is generally too little left for a relevant investigation. Here we perform some experiments in order to find a method
for fine-classification of A stars, both normal and chemically peculiar, within the framework of the M K system.
In this connection it is desirable to reduce the present multitude of CP classifications to a manageable number. It is shown
here that, independenttly of the definition of the degree of peculiarity, there is no sharp borderline separating the CP stars
from the ‘normal’ ones.
Also it is found that spectral classification can on an average be performed with almost the same accuracy for CP stars as
for the ‘normal’ ones provided cases of extreme peculiarity are avoided.
Based on observations collected at European Southern Observatory, La Silla, Chile. 相似文献
17.
Symbiotic stars that are strong radio sources and have cool dust emitting in the infrared are expected to have extended emission
nebulae around them. In order to search for such emission nebulae, we have carried out CCD imaging of three symbiotic stars
(R Aqr, RR Tel and H1-36) with narrow-band filters centred at the emission lines of [O III] λ5007, Hα λ6563, [N II] λ6584,
[S II] λ6717 + 6731. RR Tel and H1-36 images do not show any extended nebulosities around them. The CCD image of the R Aqr
nebulosity in the high excitation [O m] line is different from its image in Hα and the low excitation lines of [N II] and
[S II] indicating ionization-stratification in the nebula. In H1-36 the optical nebulosity (if it exists) is smaller than
∽2 arcsec while the radio image size is known to be large (∽5 arcsec). This behaviour is opposite to that seen in R Aqr in
which the radio emission comes from the core region of a much larger optical nebulosity. Interstellar and/or circumstellar
extinctions are suggested to be responsible for this difference 相似文献
18.
S. K. Balayan 《Astrophysics》1997,40(4):413-415
A brief analysis of a sample of stars from the Second Byurakan Spectroscopic Survey is given. It contains 626 objects in the
range of apparent magnitudes 10.1 ≤ m(pg) ≤ 19.5 and consists mainly of white dwarfs and subdwarfs of early spectral types.
Most of the objects have been classified for the first time. Their distributions with respect to stellar magnitude and spectral
type are given.
Translated from Astrofizika, Vol. 40, No. 4, pp. 627–631, October-December, 1997. 相似文献
19.
Blue Supergiants (BSGs) are the brightest stars in the universe at visual light with absolute magnitudes up to M V =−10 mag. They are ideal stellar objects for the determination of extragalactic distances, in particular, because the perennial uncertainties troubling most of the other stellar distance indicators, interstellar extinction and metallicity, do not affect them. The quantitative spectral analysis of low resolution spectra of individual BSGs provides accurate stellar parameters and chemical composition, which are then used to determine accurate reddening and extinction from photometry for each individual object. Accurate distances can be determined from stellar gravities and effective temperatures using the “Flux Weighted Gravity–Luminosity Relationship (FGLR)”. 相似文献
20.
H. V. Abrahamyan 《Astrophysics》2007,50(4):488-499
A catalog of 995 C and late M type stars is compiled from the First Byurakan Survey of the sky (FBS). The question of effectively
separating giants and dwarfs among the stars of spectral class M is examined using data from this catalog, the 2MASS survey,
and a number of other catalogs. This has made it possible to determine the luminosity class of 846 class M stars from the
FBS survey. In the sample of FBS late M stars, 187 are dwarfs and 659 are giants. The sample of FBS late M stars is compared
statistically with the set of known samples of type M stars. The subsample of FBS M-giants is proved to be similar to Stephenson’s
standard sample of M-giants. A detailed statistical analysis of these two samples is carried out.
__________
Translated from Astrofizika, Vol. 50, No. 4, pp. 589–602 (November 2007). 相似文献