共查询到20条相似文献,搜索用时 15 毫秒
1.
D. R. Alexander F. Allard A. Tamanai P. H. Hauschildt 《Astrophysics and Space Science》1997,251(1-2):171-175
We have constructed a grid of model atmospheres for cool dwarf stars and brown dwarfs with Teff ≤ 3000 K that includes (i) an equation of state which accounts for over 600 gas phase species and 1000 liquids and solids,
and (ii) the opacities of corundum (Al2O3), iron, enstatite (MgSiO3) and forsterite (Mg2SiO4), as well as amorphous carbon and SiC. We confirm earlier findings of Tsuji, Ohnaka & Aoki (1996a) that grains are abundant
in the outer photospheric layers of red and brown dwarfs with spectral type later than M8. We identify high temperature condensates
including perovskite (CaTiO3) that depletes the photospheres of important absorbers including TiO, and we confirm the disappearance of TiO bands in the
observed spectra of cool dwarfs.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
2.
We present new ultraviolet spectra of the hottest known, peculiar white dwarf H1504+65, obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. H1504+65 is the hottest known white dwarf (T
eff=200 000 K) and has an atmosphere mainly composed by carbon and oxygen, augmented with high amounts of neon and magnesium.
This object is unique and the origin of its surface chemistry is completely unclear. We probably see the naked core of either
a C–O white dwarf or even a O–Ne–Mg white dwarf. In the latter case, this would be the first proof that such white dwarfs
can be the outcome of single-star evolution. The new observations were performed to shed light on the origin of this mysterious
object. 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.
Results from a spectral study of the quasar Kaz 102 are presented. It is shown that its spectrum varies as a whole; that is,
the parameters of both the lines and the continuum change. Based on a comparison of results presented previously and in this
paper, it is concluded that over a time of approximately 27.5 years the equivalent widths and relative intensities of the
lines have increased, while their half widths have decreased. The spectral composition of Kaz 102 has also changed: new lines,
HeII λ4686, [OIII] λ4363, and others, appear in spectra of 2000 and 2001 which were not observed in spectra taken in 1973.
The electron density, and the mass and effective radius of the gas component are determined to be 2·107 cm-3, 2·104 M⊙, and 0.2 pc.
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Translated from Astrofizika, Vol. 50, No. 2, pp. 161–170 (May 2007). 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.
High dispersion CCD spectra are used to study the profiles of the Hα and Hβ lines of 48 stars in early spectral classes in
the young diffuse binary cluster h/χ Per. In addition, moderate resolution spectra of 15 B and Be stars were taken over the
interval 4400–4960 Å. One or, possibly, two new Be stars are discovered. The major parameters of the Hα line are measured
for the observed B and Be stars. The spectra over 4400–4960 Å are used to estimate Teff, logg, and υsin i. No traces of emission are detected in the Hα line profiles for 28 of the stars and emission is observed in the Hα line
for 20. During our observations an absorption profile of the Hα line was observed for some of the stars, such as Oo146, Oo566,
Oo922, and Oo1268, although they have previously been identified as Be stars. A significant long-term variability of the Hα
line is discovered for the Be stars Oo1161 and Oo2242. Oo2371 manifests a variability in its faint emission spectrum which
is typical of close binary systems that include a Be star.
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Translated from Astrofizika, Vol. 51, No. 2, pp. 305–319 (May 2008). 相似文献
7.
The ages of 224 eclipsing variable stars from the catalogue by M. Svechnikov and E. Perevozkina, which lie on the Main Sequence,
are computed in two independent manners – isochrone method and evolutionary track method. The effect of errors in the initial
parameters up onstellar ages computed within L-Teff, M-R and Teff-g diagrams are discussed. Comparisons with the results obtained by other authors are made and satisfactory agreements are
achieved.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
We present the theoretical analysis of the Al I line formation in the spectra of late-type stars ignoring the assumption of
local thermodynamic equilibrium (LTE). The calculations were based on the 39-level aluminum atom model for one-dimensional
hydrostatic stellar atmosphere models with the parameters: T
eff from 4000 to 9000 K, log g = 0.0–4.5, and metallicity [A] = 0.0;–1.0;–2.0;–3.0;–4.0. The aluminum atom model and the method of calculations were tested by the study of line profiles
in the solar spectrum. We refined the oscillator strengths and Van-der-Vaals broadening constants C
6 of the investigated transitions. We conclude that the Al I atom is in the overionization state: the 3p level is underpopulated in the line formation region. This leads to the line weakening, as compared with the LTE results.
The overionization effect becomes more pronounced with increasing temperature and decreasing metallicity. We show that the
use of various atomic data (ionization cross-sections) for the low levels of Al I does not change the behavior of non-LTE
deviations, whereas the value of these deviations varies essentially. For nine selected Al I lines we calculated the grids
of theoretical non-LTE corrections (ΔX
NLTE = logɛ
NLTE − log ɛ
LTE) to the Al abundances determinedwith the LTE assumption. The non-LTE corrections are positive and significant for the stars
with temperatures T
eff > 6000 K. These corrections weakly depend on log g, and increase with declining stellar metallicity. 相似文献
9.
María Rosa Zapatero Osorio José Caballero Eduardo L. Martín Víctor J.S. Béjar Rafael Rebolo 《Astrophysics and Space Science》2004,292(1-4):673-679
We have monitored S Ori 45, a young, low-mass (20 M j up) brown dwarf of the σ Orionis cluster (~3 Myr, 352 pc), using optical and near-infrared filters. S Ori 45 (spectral type M8.5) is found to be multi-periodic with a dominant modulation at 2.5–3.5 h, and a short modulation at about 46 min. We ascribe the longer of these modulations to a rotation period. After comparing these results with observations of more massive cluster brown dwarfs and field brown dwarfs, we conclude that substellar objects present rotational and angular momentum evolution. We have also obtained intermediate-resolution near-infrared spectroscopy of S Ori 70, which is a T-class, free-floating planetary candidate member in the σ Orionis cluster. Its observed spectrum has been compared to data of field brown dwarfs of similar types and to theoretical spectra computed for different surface temperatures and gravities. We conclude that S Ori 70 has a significantly cool, low-gravity atmosphere. This supports the young age of this object and its membership in the cluster. From state-of-the-art evolutionary models, the mass of S Ori 70 is estimated at 3 times the Jovian mass (+5 ?2 M j up), challenging current stellar/substellar formation models. S Ori 70 remains the lowest mass object so far identified in any open cluster. 相似文献
10.
Cross correlations between observed and synthetic spectra are used to discover yet another satellite of BM Ori with the following
characteristics: effective temperature Teff = 4000 K, radius R = 16R⊙, mass M = 1.8M⊙, spectral type K7 III, absolute bolometric stellar magnitude Mb = + 4m·0, axial rotation velocity V sini = 85 km/s, and relative luminosity 0.005 near the V band.
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Translated from Astrofizika, Vol. 49, No. 1, pp. 111–120 (February 2006). 相似文献
11.
We report on the results of the spectroscopy of 10 objects previously classified as brown dwarf candidates via RIJHK colors by Eisenbeiss et al. (2009), who performed deep imaging observations on a ∼0.4 sq.deg. field at the edge of the Pleiades. We describe and judge on classification techniques in the region of M‐type stars. To classify and characterise the objects, visual and near infrared spectra have been obtained with VLT FORS and ISAAC. The spectral classification was performed using the shape of the spectra as well as spectral indices that are sensitive to the spectral type and luminosity class of M‐type stars and late M‐type brown dwarfs. Furthermore a spectrophotometric distance was calculated and compared the distance of the Pleiades to investigate the membership probability. As a second argument we analyzed the proper motion. The brown dwarf candidates were found not to be brown dwarfs, but late‐K to mid‐M‐type dwarf stars. Based on the obtained distance and tabulated proper motions we conclude that all objects are background dwarf stars (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
The effective temperatures Teff, gravitational force g at the stellar surface, and Fe/H have been calculated for 50 components of 15 Trapezia of early spectral
types from electrophotometric observations in the six-color uvbyβ photometric system. The results of the calculation showed
that the log Teff of Trapezia components lie in the range 4.03–4.54, while their log g lie in the range 2.58–4.02. The atmospheric parameters
Teff and g were used to determine the stars’ masses and ages based on Hejlesen’s calculated evolutionary model sequences. All
the Trapezia components have several times more mass than the sun and almost half of them have over 10 times that mass. Over
70% of the components are less than 40.106 years old.
Translated from Astrofizika, Vol. 41. No. 2. pp. 235–244, April-June, 1998. 相似文献
13.
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
14.
A technique for determining the effective temperature T
eff
and the acceleration of gravity log g of F and G supergiants is discussed using four bright stars as examples, specifically two F supergiants, α Lep(F0 Ib) and
π Sgr (F2 II), and two G supergiants, β Aqr (G0 Ib) and α Aqr (G2 Ib). In all four cases the parameter log g was derived from the high precision parallaxes recently obtained by van Leeuwen in a new reduction of data from Hipparcos.
Because of this, the accuracy of the determinations of log g is much greater than before. Estimates of the parameter T
eff
were checked using accurate values of T
eff
obtained previously by the infrared flux method (IRFM). In the case of the early F supergiants, this method confirms the
good accuracy of the T
eff
values derived from the Balmer lines and the β-index. Measurements of the Balmer lines for the G supergiants are difficult
because of strong blending, so the indices [c
1] and β serve as indicators of T
eff
. It is shown that the indices [c
1] and β yield a systematic difference in the values of T
eff
; the IRFM confirms that deriving T
eff
from the index [c
1] is more accurate. Based on the values of T
eff
and log g that have been found here, with the aid of the evolutionary tracks, we estimate the mass M and age t of each star. The Fe II lines, which are insensitive to departures from LTE, have been used to determine the microturbulence
parameter V
t
and the iron abundance. The latter is close to the solar iron abundance. Some problems concerning the chemical composition
of these stars are discussed using the supergiant α Lep as an example.
Translated from Astrofizika, Vol. 52, No. 2, pp. 237–257 (May 2009). 相似文献
15.
We have used the 40 cm coronagraph with an inverse occulting disk to observe the limb darkening free of instrumental stray
light. Our results agree remarkably well with those of Petro et al. (1984, Astrophys. J.
283, 426) who used the McMath – Pierce tower telescope but employed a different correction procedure for instrumental stray light
than Neckel and Labs (1994, Solar Phys.
153, 91), whose results for λ=445.1 nm deviate systematically, apparently overcorrecting for stray light. Future continuation of such highly reproducible
measurements offers an interesting independent diagnostic of possible slow trends in effective temperature (T
eff) and in total solar irradiance. 相似文献
16.
Claus Tappert Boris T. Gänsicke Ronald E. Mennickent Linda Schmidtobreick 《Astrophysics and Space Science》2006,304(1-4):299-301
We present preliminary results on spectroscopic data of the candidate pre-cataclysmic variable LTT 560. A fit to the flux-calibrated spectrum reveals the temperature of the white-dwarf primary to be T
eff=7000–7500 K, and confirms the result of previous studies on the detection of an M5V secondary star. The analysis of radial velocity data from spectral features attributed to the primary and the secondary star show evidence for low-level accretion. 相似文献
17.
Tokio Tsubaki 《Solar physics》1975,43(1):147-175
A technique developed for analysing line profiles with both speed and high accuracy was used to study the physical conditions
of a coronal formation near a quiescent prominence. Detailed analyses of five coronal lines (Fe xiv λ 5303, Fe x λ 6374, Ni xv λ 6702, Fe xv λ 7059, and Fe xi λ 7892) provided total intensities, Doppler width temperatures, ionization temperatures, and velocities.
Dissimilar spatial fluctuations in intensity are obvious for ions grouped according to (low vs high) ionization potentials.
The intensity of the green line shows a local minimum around the observed quiescent prominence; a corresponding but much more
diffuse pattern is visible in the red line intensity.
Large differences are observed in temperatures derived by different means. In particular,
, while
, and
. The differences between
and
are taken as direct evidence of temperature inhomogeneity. One can thus put little significance in T
e
(xi/x). T
D(λ5303) and T
e
(xv/xiv) fluctuate nearly in parallel at each slit height, with a weak local minimum evident around the prominence. The discrepancy
between these two can be removed if a non-thermal turbulent motion of 6–16 km s−1 is assumed. Variations with height of both T
D(λ5303) and T
e
(xv/xiv) suggest that the coronal temperature maximum is located no more than 15000 km above the top of spicules. A negative gradient
of about 6 deg km−1 is found in the height variation of T
D(λ5303).
The height variation of the green line wavelength shows that the majority of coronal material in this region is flowing from
west to east on the Sun, with the highest velocity of 12 km s−1 found at the lowest heights. This motion is in the same sense as that of the nearby coronal rain, as determined both from
the spectra and wavelength-shifted Hα filtergrams. Superposed on the above flow is a systematic velocity field of up to ±5
km s−1. This field similarly reaches maximum amplitudes at lowest heights showing a local maximum around the prominence.
On leave from Institute of Earth Science and Astrophysics, Shiga University, Ohtsu 520, Japan, as 1973–75 National Academy
of Science/National Research Council Senior Post-Doctoral Research Associate at Sacramento Peak Observatory. 相似文献
18.
E. L. Karapetyan 《Astrophysics》2006,49(3):299-305
Spectral observations of 19 galaxies with UV-excesses from Kazarian’s list are reported. The spectra were obtained with the
2.6-m telescope at the Byurakan Observatory using the SCORPIO spectral camera. A grism was used to obtain spectra in the wavelength
interval λλ7420-3920 Å. 43 spectra in which emission lines are mainly observed were obtained from the 19 galaxies, except
for the spectra of Kaz 21, Kaz 178, Kaz 183, and Kaz 184. The spectra of Kaz 17, Kaz 151, Kaz 153, and Kaz 357 have type Sy2
galactic features. In the spectra of the galaxies Kaz 17, Kaz 151, and Kaz 153, absorption lines are observed along with high
excitation emission lines such as HeI λ5876 Å and HeII λ4686 Å. No lines were observed within the interval λλ7420-3920 Å in
the spectra of the galaxies Kaz 183 and Kaz 184.
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Translated from Astrofizika, Vol. 49, No. 3, pp. 351–358 (August 2006). 相似文献
19.
K. R. Covey T. P. Greene G. W. Doppmann C. J. Lada B. A. Wilking 《Astronomische Nachrichten》2005,326(10):886-890
Recent observations of nearby star forming regions have offered evidence that young brown dwarfs undergo a period of mass accretion analogous to the T Tauri phase observed in young stars. Brown dwarf analogs to stellar protostars, however, have yet to be definitively observed. These young, accreting objects would shed light on the nature of the dominant brown dwarf formation process, as well as provide ideal laboratories to investigate the dependence of the accretion mechanism on protostellar mass. Recent near infrared surveys have identified candidate proto‐brown dwarfs and characterized low mass protostars in nearby star forming regions. These techniques allow near infrared spectra to diagnose the effective temperature, accretion luminosity, magnetic field strength and rotation velocity of young low mass stars across the stellar/substellar boundary. The lowest mass proto‐brown dwarfs (M < 40 MJup), however, will prove challenging to observe given current near IR observational capabilities. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
We present the spectral analysis of the physical state and evolution of the WZSge-type cataclysmic variable GSC02197-00886. The spectra of the system, covering the total orbital period at the time of the outburst on May 8, 2010, at the late relaxation stage, and in the quiescent state, were obtained at the SAO RAS 6-m BTA telescope in 2010–2012. From the absorption and emission HI, He I, and Fe II lines, we have determined the radial velocities for all the nights of observations and constructed the maps of Doppler tomography for the quiescent state. It was found that during the outburst the spectra of the object were formed in an optically thick accretion disk with an effective temperature of T eff ≈ 45 000 K and in a hotter boundary layer. During the relaxation of the system, the accretion disk gradually became optically thinner in the continuum and in the emission lines. In the quiescent state (July 2012), the continuous spectrum was dominated by the radiation of the cooling white dwarf with T eff = 18 000 K. The emission lines are formed on the surface of the cool star by the X-ray irradiation of the 1RXSJ213807.1+261958 source. We propose a method for determining the parameters of the white dwarf, based on the numerical modeling of the system spectra in the quiescent state and their comparison with the observed spectra. It is shown that the effective temperature of white dwarf has decreased by ΔT eff = 6000 K during the relaxation from August 2010 to July 2012. We have obtained a set of parameters for GSC02197-00886 and shown their good agreement with the average parameters of the W Z Sge-type systems, presented in the literature. 相似文献