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1.
The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations, for a total of more
than 60 000 ultraviolet spectra. We have determined statistical properties of the sample of GALEX stars. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution and we have employed it to determine the atmospheric parameters of stars in the range 4500≲ T
eff≲9000 K. Our preliminary results indicate that the majority of the sample is formed by main sequence F- and G-type stars,
with metallicity [M/H]≳−1 dex. 相似文献
2.
The problem of lithium in chemically peculiar Ap-CP stars has been the subject of debate for many years. The main reason for
this is a lack of spectral observations of Ap stars in the neighborhood of the lithium resonance doublet Li I 6708 Å. An international
cooperation project on “Lithium in cool CP stars with magnetic fields” was started in 1996. Systematic observations of CP
stars in spectral regions of the 6708 Å and 6103 Å lines at the ZTSh (CrAO), CAT (ESO), Feros (ESO), and the 74″ telescope
of the Mount Stromlo Observatory (Australia) have been used to analyze spectra of several CP stars studied by the way the
6708 Å lithium line varies with the stars’ rotational phase. Monitoring of the spectra of the oscillating CP stars (group
I) HD 83368, HD 60435, and HD 3980, for which significant Doppler shifts of the Li I 6708 Å line are observed led to the discovery
of “lithium spots” on the surface of these stars whose positions are related to the magnetic field structure. Models of the
surfaces of these stars with the special program “ROTATE” based on the profiles of the Li I 6708 Å line are used to estimate
the size of the spots, their positions on the stars’ surface, and the lithium abundances in these spots. A detailed analysis
and modelling of the spectra of slowly rotating oscillating CP stars with strong, invariant lithium 6708 Å emission, including
blending with lines of the rare earth elements, reveals an enhanced lithium abundance, with the abundance determined from
the lithium 6103 Å line being higher than that determined from the 6708 Å line for all the stars. This may indicate vertical
stratification of lithium in the atmospheres of CP stars with an anomalous isotopic composition ( 6Li/ 7Li = 0.2–0.5). HD 101065, an ultraslow rotator (v sini ≈ 1.5) visible from the poles and with powerful oscillations which cause pulsating line broadening in its spectrum, is unique
among these stars. The amount of lithium in the atmosphere of HD 101065 log N(Li) = 3.1 on a scale of log N(H) = 12.0 and the isotope ratio 6Li/ 7Li ≈ 0.3. The high estimates of 6Li/ 7Li may be explained by the production of lithium in spallation reactions and the preservation of surface 6Li and 7Li by strong magnetic fields in the upper layers of the atmosphere near the magnetic poles.
__________
Translated from Astrofizika, Vol. 50, No. 3, pp. 463–492 (August 2007). 相似文献
3.
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 C 2 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 lg N(Li) ≈ 2, −1.4, and −0.9, respectively. Discrepancies of lithium abundances lg N(Li) obtained with the help of molecular line lists do not seem to exceed 0.2 dex. 相似文献
4.
The Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) X-ray data base (February 2002 – May 2006) has been searched to find solar flares with weak thermal components and
flat photon spectra. Using a regularized inversion technique, we determine the mean electron flux distribution from count
spectra for a selection of events with flat photon spectra in the 15 – 20 keV energy range. Such spectral behavior is expected
for photon spectra either affected by photospheric albedo or produced by electron spectra with an absence of electrons in
a given energy range ( e.g., a low-energy cutoff in the mean electron spectra of nonthemal particles). We have found 18 cases that exhibit a statistically
significant local minimum (a dip) in the range of 13 – 19 keV. The positions and spectral indices of events with low-energy
cutoff indicate that such features are likely to be the result of photospheric albedo. It is shown that if the isotropic albedo
correction is applied, all low-energy cutoffs in the mean electron spectrum are removed, and hence the low-energy cutoffs
in the mean electron spectrum of solar flares above ∼ 12 keV cannot be viewed as real features. If low-energy cutoffs exist
in the mean electron spectra, their energies should be less than ∼ 12 keV. 相似文献
5.
Stochastic temperatures and turbulence are characterized by average velocities u
th
and < u
turb
> ≡ u
0 and fluctuations u¢th {u'_{th}} and u′ (<u′ > = 0). Thus, the Doppler width of a line also has a fluctuating component Dl¢D \Delta {\lambda '_D} . Observed spectra correspond to the radiative flux averaged over time and over a star’s surface, <Hλ>. Usually, only the average velocities u
th
and u
0 are taken into account in photospheric models and these yield the Doppler width DlD(0) \Delta \lambda_D^{(0)} of a line in the customary way. The fluctuations Dl¢D \Delta {\lambda '_D} mean that near a line center the average absorption coefficient < αλ > is larger than the usual αλ, which depends only on the average velocities u
th
and u
0. This enhances the absorption line near the center and is not explained by the photospheric models. This new statistical
effect depends on the wavelength of the line. A comparison of observed lines with model profiles yields an estimate for the
average level of fluctuations in the Doppler width, h =
á | Dl¢D |
ñ | / |
DlD(0) \eta = {{{\left\langle {\left| {\Delta {{\lambda '}_D}} \right|} \right\rangle }} \left/ {{\Delta \lambda_D^{(0)}}} \right.} , which characterizes the average stochasticity of a photosphere and is important for understanding the physics of photospheres.
The depths of lines in synthetic spectra of stars are often greater than the observed values. The observed disagreement between
the theoretical and actually observed depths of lines can be corrected by introducing an additional parameter, the fluctuation
level η. Then it is possible to obtain estimates of η for a number of stars. 相似文献
6.
Comparisons of solar magnetic-field measurements made in different spectral lines are very important, especially in those
lines in which observations have a long history or (and) specific diagnostic significance. The spectral lines Fe i 523.3 nm and Fe i 525.0 nm belong to this class. Therefore, this study is devoted to a comprehensive analysis using new high-precision Stokes-meter
full-disk observations. The disk-averaged magnetic-field strength ratio R= B(523.3)/ B(525.0) equals 1.97±0.02. The center-to-limb variation (CLV) is R=1.74−2.43 μ+3.43 μ
2, where μ is the cosine of the center-to-limb angle. For the disk center, we find R=2.74, and for near-limb areas with μ=0.3, R equals 1.32. There is only a small dependence of R on the spatial resolution. Our results are rather close to those published three decades ago, but differ significantly from
recent magnetographic observations. An application of our results to the important SOHO/MDI magnetic data calibration issue
is discussed. We conclude that the revision of the SOHO/MDI data, based only on the comparison of magnetic-field measurements
in the line pair Fe i 523.3 nm and Fe i 525.0 nm (increasing by a factor of 1.7 or 1.6 on average according to recent publications) is not obvious and new investigations
are urgently needed. 相似文献
7.
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 T eff, logg, and υ sin 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.
__________
Translated from Astrofizika, Vol. 51, No. 2, pp. 305–319 (May 2008). 相似文献
8.
A list of comparatively faint late M and Carbon type stars detected on the Digitized First Byurakan Survey (DFBS) spectral
plates in the zone with +45° ≤ δ ≤ +49° covering 684 deg 2 is presented. Accurate DSS2 positions, USNO-B1.0 B and R magnitudes, 2MASS near-infrared J, H, and K s photometry, IRAS PSC/FSC fluxes (when available), approximate spectral types, and luminosity class estimates are given for
72 objects. Nine of them are newly confirmed carbon stars and 63 are M-type stars. For seven Mira variables with known pulsation
periods we determined distances of 2 ÷ 8 kpc using a period-luminosity relation. Distances of 17 ÷ 115 pc for five M dwarfs,
classified on the base of detected proper motions, were estimated using a color-luminosity relation. The object FBS 0845+466
is classified as a candidate carbon dwarf with distance r ≈ 72 pc. 相似文献
9.
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 νsin i 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
10.
Based on spectra taken with a 6-m telescope, we analyzed the abundances of chemical elements in the He-weak stars HD 21699
and HD 217833, estimated their surface magnetic fields (B s = 4000 and 4500 G, respectively) from the magnetic intensification of spectral lines, and determined their microturbulences
( V
t = 0.80 and 0.75 km s −1, respectively). The low values of V
t show that the stellar atmospheres are stabilized by a magnetic field, which explains the presence of diffusion processes
that lead to chemical anomalies. Helium is strongly underabundant, and its deficiency is −1.50 and −1.81 dex in HD 21699 and
HD 217833, respectively. We used model atmospheres to determine the effective temperatures, T
eff = 16 000 and 15 450 K, and surface gravities, log g = 4.15 and 3.88, for the stars from the Hδ line, implying that they lie on the main sequence near the stars of luminosity
class V. 相似文献
11.
We present an atlas of spectra of high signal-to-noise ratio and high spectral resolution (R ≥ 60000) in a poorly studied short-wavelength region up to 3055 Å. The spectra of well-studied stars of close temperatures ( β Ori, α Lyr and α Cyg) are compared with the spectrum of a low-metallicity A-type supergiant KSPer, the atmosphere of which is poor in hydrogen, H/He = 3 × 10 ?5.We study the velocity field in the expanding atmospheres and envelopes of these stars. A complete atlas and detailed identification of spectral features are available in the Internet. 相似文献
12.
The Molecular Hydrogen Explorer, H2 EX, was proposed in response to the ESA 2015 - 2025 Cosmic Vision Call as a medium class space mission with NASA and CSA participations.
The mission, conceived to understand the formation of galaxies, stars and planets from molecular hydrogen, is designed to
observe the first rotational lines of the H 2 molecule (28.2, 17.0, 12.3 and 9.7 μm) over a wide field, and at high spectral resolution. H2 EX can provide an inventory of warm (≥ 100 K) molecular gas in a broad variety of objects, including nearby young star clusters,
galactic molecular clouds, active galactic nuclei, local and distant galaxies. The rich array of molecular, atomic and ionic
lines, as well as solid state features available in the 8 to 29 μm spectral range brings additional science dimensions to
H2 EX. We present the optical and mechanical design of the H2 EX payload based on an innovative Imaging Fourier Transform Spectrometer fed by a 1.2 m telescope. The 20’×20’ field of view
is imaged on two 1024×1024 Si:As detectors. The maximum resolution of 0.032 cm − 1 (full width at half maximum) means a velocity resolution of 10 km s − 1 for the 0 – 0 S(3) line at 9.7 μm. This instrument offers the large field of view necessary to survey extended emission in
the Galaxy and local Universe galaxies as well as to perform unbiased extragalactic and circumstellar disks surveys. The high
spectral resolution makes H2 EX uniquely suited to study the dynamics of H 2 in all these environments. The mission plan is made of seven wide-field spectro-imaging legacy programs, from the cosmic
web to galactic young star clusters, within a nominal two years mission. The payload has been designed to re-use the Planck platform and passive cooling design.
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 T warm ∼ 1000K and T cold ∼ 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.
The PLAnetary Transits and Oscillations of stars Mission (PLATO), presented to ESA in the framework of its “Cosmic Vision” programme, will detect and characterize exoplanets
by means of their transit signature in front of a very large sample of bright stars, and measure the seismic oscillations
of the parent stars orbited by these planets in order to understand the properties of the exoplanetary systems. PLATO is the
next-generation planet finder, building on the accomplishments of CoRoT and Kepler: i) it will observe significantly more stars, ii) its targets will be 2 to 3 magnitudes brighter (hence the precision of the measurements will be correspondingly greater
as will be those of post-detection investigations, e.g. spectroscopy, asteroseismology, and eventually imaging), iii) it will be capable of observing significantly smaller exoplanets. The space-based observations will be complemented by ground-
and space-based follow-up observations. These goals will be achieved by a long-term (4 years), high-precision, high-time-resolution,
high-duty-cycle monitoring in visible photometry of a sample of more than 100,000 relatively bright (m
V
≤ 12) stars and another 400,000 down to m
V
= 14. Two different mission concepts are proposed for PLATO: i) a “staring” concept with 100 small, very wide-field telescopes, assembled on a single platform and all looking at the same 26° diameter field,
and ii) a “spinning” concept with three moderate-size telescopes covering more than 1400 degree 2.
See for The PLATO Consortium. 相似文献
15.
I have compiled here the three libraries of high and mid-resolution optical spectra of late-type stars I have recently published.
The libraries include F, G, K and M field stars, from dwarfs to giants. The spectral coverage is from 3800 to 1000 Å, with
spectral resolution ranging from 0.09 to 3.0 Å. These spectra include many of the spectral lines most widely used as optical
and near-infrared indicators of chromospheric activity. The spectra have been obtained with the aim of providing a library
of high and mid-resolution spectra to be used in the study of active chromosphere stars by applying a spectral subtraction
technique. However, the data set presented here can also be utilized in a wide variety of ways. A digital version of all the
fully reduced spectra is available via FTP and the World Wide Web (WWW) in FITS format.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
We applied special data-processing algorithms to the study of long-period oscillations of the magnetic-field strength and
the line-of-sight velocity in sunspots. The oscillations were investigated with two independent groups of data. First, we
used an eight-hour-long series of solar spectrograms, obtained with the solar telescope at the Pulkovo Observatory. We simultaneously
measured Doppler shifts of six spectral lines, formed at different heights in the atmosphere. Second, we had a long time series
of full-disk magnetograms (10 – 34 hour) from SOHO/MDI for the line-of-sight magnetic-field component. Both ground- and space-based
observations revealed long-period modes of oscillations (40 – 45, 60 – 80, and 160 – 180 minutes) in the power spectrum of
the sunspots and surrounding magnetic structures. With the SOHO/MDI data, one can study the longer periodicities. We obtained
two new significant periods (> 3 σ) in the power spectra of sunspots: around 250 and 480 minutes. The power of the oscillations in the lower frequencies is
always higher than in the higher ones. The amplitude of the long-period magnetic-field modes shows magnitudes of about 200 – 250 G.
The amplitude of the line-of-sight velocity periodicities is about 60 – 110 m s −1. The absence of low-frequency oscillations in the telluric line proves their solar nature. Moreover, the absence of low-frequency
oscillations of the line-of-sight velocity in the quiet photosphere (free of magnetic elements) proves their direct connection
to magnetic structures. Long-period modes of oscillation observed in magnetic elements surrounding the sunspot are spread
over the meso-granulation scales (10″ – 12″), while the sunspot itself oscillates as a whole. The amplitude of the long-period
mode of the line-of-sight velocity in a sunspot decreases rapidly with height: these oscillations are clearly visible in the
spectral lines originating at heights of approximately 200 km and fade away in lines originating at 500 km. We found a new
interesting property: the low-frequency oscillations of a sunspot are strongly reduced when there is a steady temporal trend
(strengthening or weakening) of the sunspot’s magnetic field. Another important result is that the frequency of long-period
oscillations evidently depends on the sunspot’s magnetic-field strength. 相似文献
17.
We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent
timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the
“Solar X-ray Spectrometer” (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May
2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F( ε) from the flare by integrating a series of isothermal plasma flux. We find that the multi-temperature integrated flux F( ε) is a power-law function of ε with a spectral index ( γ)≈−4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E=4 – 15 keV is dominated by temperatures of T=12 – 50 MK, while the multi-thermal power-law DEM index ( δ) varies in the range of −4.4 and −5.7. The temporal evolution of the X-ray flux F( ε, t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling
time varies between 296 and 4640 s and the electron density ( n
e) varies in the range of n
e=(1.77 – 29.3)×10 10 cm −3. Employing temporal evolution technique in the current study as an alternative method for separating thermal from nonthermal
components in the energy spectra, we measure the break-energy point, ranging between 14 and 21±1.0 keV. 相似文献
18.
We present the results of studying the spectral and photometric variability of the luminous blue variable star V532 in M33.
The photometric variations are traced from 1960 to 2010, spectral variations—from 1992 to 2009. The star has revealed an absolute
maximum of visual brightness (1992–1994, high/cold state) and an absolute minimum (2007–2008, low/hot state) with a brightness
difference of ΔB ≈ 2.3
m
. The temperature estimates in the absolute maximum and absolute minimum were found to be T ∼ 22000 K and T ∼ 42000 K, respectively. The variability of the spectrum of V532 is fully consistent with the temperature variations in its
photosphere, while both permitted and forbidden lines are formed in an extended stellar atmosphere. Broad components of the
brightest lines were found, the broadening of these components is due to electron scattering in the wind parts closest to
the photosphere. We measured the wind velocity as a difference between the emission and absorption peaks in the PCyg type
profiles. The wind velocity clearly depends on the size of the stellar photosphere or on the visual brightness, when brightness
declines, the wind velocity increases. In the absolute minimum a kinematic profile of the V532 atmosphere was detected. The
wind velocity increases and its temperature declines with distance from the star. In the low/hot state, the spectral type
of the star corresponds to WN8.5h, in the high/cold state—to WN11. We studied the evolution of V532 along with the evolution
of AGCar and the massive WR binary HD5980 in SMC. During their visual minima, all the three stars perfectly fit with the WNL
star sequence by Crowther and Smith (1997). However, when visual brightness increases, all the three stars form a separate
sequence. It is possible that this reflects a new property of LBV stars, namely, in the high/cold states they do not pertain
to the bona fide WNL stars. 相似文献
19.
An experiment was conducted in conjunction with the total solar eclipse on 29 March 2006 in Libya to measure both the electron
temperature and its flow speed simultaneously at multiple locations in the low solar corona by measuring the visible K-coronal
spectrum. Coronal model spectra incorporating the effects of electron temperature and its flow speed were matched with the
measured K-coronal spectra to interpret the observations. Results show electron temperatures of (1.10±0.05) MK, (0.70±0.08) MK,
and (0.98±0.12) MK, at 1.1 R
⊙ from Sun center in the solar north, east and west, respectively, and (0.93±0.12) MK, at 1.2 R
⊙ from Sun center in the solar west. The corresponding outflow speeds obtained from the spectral fit are (103±92) km s −1, (0+10) km s −1, (0+10) km s −1, and (0+10) km s −1. Since the observations were taken only at 1.1 R
⊙ and 1.2 R
⊙ from Sun center, these speeds, consistent with zero outflow, are in agreement with expectations and provide additional confirmation
that the spectral fitting method is working. The electron temperature at 1.1 R
⊙ from Sun center is larger at the north (polar region) than the east and west (equatorial region). 相似文献
20.
Ly α and Ly β line profiles in a solar prominence were observed with high spatial and spectral resolution with SOHO/SUMER.
Within a 60-arcsec scan, we measure a very large variety of profiles: not only reversed and nonreversed profiles but also
red-peaked and blue-peaked ones in both lines. Such a spatial variability is probably related to both the fine structure in
prominences and the different orientations of mass motions. The usage of integrated-intensity cuts along the SUMER slit allowed
us to categorize the prominence in three regions. We computed average profiles and integrated intensities in these lines in
the range 2.36 – 42.3 W m −2 sr −1 for Ly α and 0.027 – 0.237 W m −2 sr −1 for Ly β. As shown by theoretical modeling, the Ly α/Ly β ratio is very sensitive to geometrical and thermodynamic properties
of fine structure in prominences. For some pixels, and in both lines, we found agreement between observed intensities and
those predicted by one-dimensional models. But a close examination of the profiles indicated a rather systematic disagreement
concerning their detailed shapes. The disagreement between observations and thread models (with ambipolar diffusion) leads
us to speculate about the importance of the temperature gradient between the cool and coronal regions. This gradient could
depend on the orientation of field lines as proposed by Heinzel, Anzer, and Gunár ( Astron. Astrophys.
442, 331, 2005). 相似文献
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