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1.
We investigate the plausibility of using diffuse interstellar band at862 nm for tracing interstellar extinction with the ESA's
astrometric space mission GAIA. For this purpose we perform numerical tests to simulate the conditions of real observations,
covering a wide range of stellar parameters and different amounts of interstellar extinction. Our simulations indicate that
with the present Radial Velocity Spectrometer setup the uncertainty in color excess of σE(B-V)≤ 0.05 can be achieved only for the interstellar reddening tracers brighter than V ∼ 13. None of the plausible tracers can provide accurate color excesses (σ
E(B-V)
≤ 0.05) at the distances beyond 2 kpc. We therefore conclude that with the currently planned instrumentation onboard GAIA
this method can not be used as a stand-alone approach for probing interstellar extinction on the Galactic distance scales
within the framework of the GAIA mission.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
G. A. Gontcharov 《Astronomy Letters》2010,36(8):584-595
The first results of the construction of a three-dimensional reddening map for stars within 1600 pc of the Sun are presented.
Analysis of the distribution of 70 million stars from the 2MASS catalog with the most accurate photometry on the (J-Ks)-Ks diagram supplemented with Monte Carlo simulations has shown that one of the maxima of this distribution corresponds to F-type
dwarfs and subgiants with a mean absolute magnitude M
Ks
= 2⊙
m
5. The shift of this maximum toward large J-Ks with increasing Ks reflects the reddening of these stars with increasing heliocentric distance. The distribution of the sample of stars over
Ks, l, and b cells with a statistically significant number of stars in each cell corresponds to their distribution over three-dimensional
spatial cells. As a result, the reddening E(J-Ks) has been determined with an accuracy of 0·
m
03 for spatial cells with a side of 100 pc. All of the known large absorbing clouds within 1600 pc of the Sun have manifested
themselves in the results obtained. The distances to the near and far edges of the clouds have been determined with a relative
accuracy of 15%. The cases where unknown clouds are hidden behind known ones on the same line of sight have been found. The
distance dependence of reddening is considered for various Galactic latitudes and longitudes. The absorbing matter of the
Gould Belt is shown to manifest itself at latitudes up to 40° and within 600 pc of the Sun. The size and influence of the
Gould Belt may have been underestimated thus far. The absorbing matter at latitudes up to 60° and within 1600 pc of the Sun
has been found to be distributed predominantly in the first and second quadrants in the southern hemisphere and in the third
and fourth quadrants in the northern hemisphere. The warping of the absorbing layer in the near Galaxy apparently manifests
itself in this way. A nonrandom orientation of the clouds relative to the Sun is possible. The mass of the baryonic dark matter
in solar neighborhoods can then be considerably larger than is generally believed. 相似文献
3.
K. Černis 《Astrophysics and Space Science》1987,133(2):355-368
The dependence of interstellar extinction on distance in the direction of the dark cloud south of Merope is determined using photoelectric photometry of 93 stars in the Vilnius photometric system. The cloud front edge is detected at 120–130 pc from the Sun and the distance of the Pleiades cluster is found to be 127 pc. Mean extinctionA
V in the Merope cloud is of the order of 1.0 mag. There is no evidence of extinction at distances exceeding the Merope cloud distance. Variable extinction method yieldsR=A
V/EB-V=3.6, while the maximum polarization wavelength method gives the value 3.4. Some Pleiades stars are suspected to be unresolved binaries. 相似文献
4.
Arūnas Kučinskas Vladas Vansevičius Toshihiko Tanabé 《Astrophysics and Space Science》2002,280(1-2):151-157
We discuss a possible use of the asymptotic giant branch (AGB) stars for tracing star formation histories on the Galactic
and extragalactic distance scales with the ESA's astrometric space mission GAIA. Extensive numerical simulations demonstrate
that metallicities (Δ [M/H] ≲ 0.3) can be obtained for the AGB stars with GAIA up to the distances of ∼ 200 kpc, if no interstellar
extinction is present. Reliable population ages can be also obtained from the AGB stars if their T
eff are constrained precisely. We show that precise effective temperatures can be obtained by fitting observed spectral energy
distributions of the AGB stars with theoretical fluxes calculated from the synthetic spectra. A combination of the derived
effective temperatures with the bolometric luminosities allows to derive precise population ages for a wide range of ages
and metallicities over the large distance scales. This demonstrates that AGB stars can be employed very effectively for tracing
star formation histories with GAIA, allowing to refine the global evolutionary scenarios of stellar populations in the Milky
Way and the galaxies beyond.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
6.
David G. Turner 《Astrophysics and Space Science》2012,337(1):303-312
A reanalysis of the (seemingly very distant) open cluster Shorlin 1, the group of stars associated with WR 38 and WR 38a,
is made on the basis of existing UBV and JHK
s observations for cluster members. The 2MASS observations, in particular, imply a mean cluster reddening of E
B−V
=1.45±0.07 and a distance of 2.94±0.12 kpc. The reddening agrees with the UBV results provided that the local reddening slope is described by E
U−B
/E
B−V
=0.64±0.01, but the distance estimates in the 2MASS and UBV systems agree only if the ratio of total-to-selective extinction for the associated dust is R=A
V
/E
B−V
=4.0±0.1. Both results are similar to what has been obtained for adjacent clusters in the Eta Carinae region by similar analyses,
which suggests that “anomalous” dust extinction is widespread through the region, particularly for groups reddened by relatively
nearby dust. Dust associated with the Eta Carinae complex itself appears to exhibit more “normal” qualities. The results have
direct implications for the interpretation of distances to optical spiral arm indicators for the Galaxy at ℓ=287°–291°, in particular the Carina arm here is probably little more than ∼2 kpc distant, rather than 2.5–3 kpc distant as
implied in previous studies. Newly-derived intrinsic parameters for the two cluster Wolf-Rayet stars WR 38 (WC4) and WR 38a
(WN5) are in good agreement with what is found for other WR stars in Galactic open clusters, which was not the case previously. 相似文献
7.
Vladas Vansevičius Audrius Bridžius Ramutis Drazdys 《Astrophysics and Space Science》2002,280(1-2):31-39
We present a method and results of evaluation of the photometric systems (PSs) proposed for the GAIA mission. The method,
however, can be applied for the analysis of virtually any multicolour PS designed for the global investigation of the Galactic
stellar populations. Performance of the 1F, 2A and 3G PSs is evaluated taking into account their ability to simultaneously
determine the main stellar parameters,T
eff, log g, [M/H] and E
B-V, for a large variety of stars down to G ∼ 20. The representative Galactic stellar populations were constructed and employed for evaluation of the PSs. Despite the
fact that the 2A and 3G PSs perform significantly better than the 1F (presently adopted as a baseline PS for GAIA), we conclude
that still there is no photometric system proposed to date, which would allow to achieve the scientific objectives of the
GAIA mission.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
K. S. Dwarakanath W. M. Goss J. H. Zhao C. C. Lang 《Journal of Astrophysics and Astronomy》2004,25(3-4):129-141
We have imaged a region of ∼ 5′ extent surrounding Sgr A* in the HI 21 cm-line absorption using the Very Large Array. A Gaussian
decomposition of the optical depth spectra at positions within ∼ 2′ (∼ 5 pc at 8.5 kpc) of Sgr A* detects a wide line underlying
the many narrow absorption lines. The wide line has a mean peak optical depth of 0.32 ± 0.12 centered at a mean velocity of
V1sr = −4 ± 15 km s{−1}. The mean full width at half maximum is 119 ± 42 km s−1. Such a wide line is absent in the spectra at positions beyond ∼ 2′ from Sgr A*. The position-velocity diagrams in optical
depth reveal that the wide line originates in various components of the circumnuclear disk (radius ∼ 1.3′ ) surrounding Sgr
A*. These components contribute to the optical depth of the wide line in different velocity ranges. The position-velocity
diagrams do not reveal any diffuse feature which could be attributed to a large number of HI clouds along the line of sight
to Sgr A*. Consequently, the wide line has no implications either to a global population of shocked HI clouds in the Galaxy
or to the energetics of the interstellar medium as was earlier thought. 相似文献
9.
Photoelectric Vilnius seven-color photometry is presented and analyzed for a sample of 24 red giant branch and clump stars
in the open cluster NGC 7789. For each star we have determined photometric spectral type, absolute magnitude, interstellar
reddening, effective temperature, metallicity, and surface gravity. From averages over the stars in the sample we find the
mean reddening to the cluster E
Y−V
= 0.21± 0.02 (s.d.), or E
B−V
= 0.25, and the apparent distance modulus (m−M)
V
= 12.21± 0.10 (s.d.), which yield a distance of 1840 pc. The mean overall metallicity is found to be [Fe/H] = −0.18± 0.09
(s.d.). The clump stars, on average, appear to be slightly more metal-rich than the other red giants, which is most probably
caused by evolutionary changes of carbon and nitrogen molecular bands falling in the photometric passbands. A difference in
mass between the two groups of stars has also been detected, which suggests that the clump stars might have undergone extra
mass loss before reaching their core He-burning phase of evolution. 相似文献
10.
A. N. Gerashchenko 《Astronomy Letters》2009,35(9):625-632
We describe a method for simultaneous determination of the metallicity and interstellar reddening of globular clusters that
uses parameters of the giant branch on the V vs. (B-R) color-magnitude diagram: the slope of the giant branch, its color at the level of the horizontal branch, and the apparent
magnitude V of the horizontal branch. Applying this method to the globular cluster NGC 7006 gives the metallicity [Fe/H] = −1.78 ± 0.11
and interstellar reddening E
B-R
= 0.25 ± 0.02. 相似文献
11.
G. A. Gontcharov 《Astronomy Letters》2013,39(8):550-560
The joint use of accurate near- and mid-infrared photometry from the 2MASS and WISE catalogues has allowed the variations of the extinction law and the dust grain size distribution in high Galactic latitudes (|b| > 50°) at distances up to 3 kpc from the Galactic midplane to be analyzed. The modified method of extrapolation of the extinction law applied to clump giants has turned out to be efficient for separating the spatial variations of the sample composition, metallicity, reddening, and properties of the medium. The detected spatial variations of the coefficientsE(H ? W1)/E(H ? Ks), E(H ? W2)/E(H ? Ks), and E(H ? W3)/E(H ? Ks) are similar for all high latitudes and depend only on the distance from the Galactic midplane. The ratio of short-wavelength extinction to long-wavelength one everywhere outside the Galactic disk has been found to be smaller than that in the disk and, accordingly, the mean dust grain size is larger, while the grain size distribution in the range 0.5–11 µm is shifted toward coarse dust. Specifically, the mean grain size initially increases sharply with distance from the Galactic midplane, then decreases gradually, approaching a value typical of the disk at |Z| ≈ 2.4 kpc, and, further out, stabilizes or may increase again. The coefficients under consideration change with coordinate Z with a period of about 1312 ± 40 pc, coinciding every 656 ± 20 pc to the south and the north and showing a significant anticorrelation between their values in the southern and northern hemispheres at intermediate Z. Thus, there exists a unified large-scale periodic structure of the interstellar medium at high latitudes within at least 5 kpc. The same periodic variations have also been found for the extinction coefficient R V within 600 pc of the Galactic midplane through the reduction of different photometric data for stars of different classes. 相似文献
12.
G. A. Gontcharov 《Astronomy Letters》2012,38(1):12-24
Multicolor photometry from the Tycho-2 and 2MASS catalogues for 11 990 OB and 30 671 K-type red giant branch stars is used
to detect systematic large-scale variations of the interstellar extinction law within the nearest kiloparsec. The characteristic
of the extinction law, the total-to-selective extinction ratio Rv, which also characterizes the size and other properties of interstellar dust grains, has been calculated for various regions
of space by the extinction law extrapolation method. The results for the two classes of stars agree: the standard deviation
of the “red giants minus OB” Rv differences within 500 pc of the Sun is 0.2. The detected Rv variations between 2.2 and 4.4 not only manifest themselves in individual clouds but also span the entire space near the
Sun, following Galactic structures. In the Local Bubble within about 100 pc of the Sun, Rv has a minimum. In the inner part of the Gould Belt and at high Galactic latitudes, at a distance of about 150 pc from the
Sun, Rv reaches a maximum and then decreases to its minimum in the outer part of the Belt and other directions at a distance of
about 500 pc from the Sun, returning to its mean values far from the Sun. The detected maximum of Rv at high Galactic latitudes is important when allowance is made for the interstellar extinction toward extragalactic objects.
In addition, a monotonic increase in Rv by 0.3 per kpc toward the Galactic center has been found near the Galactic equator. It is consistent with the result obtained
by Zasowski et al. (2009) for much of the Galaxy. Ignoring the Rv variations and traditionally using a single value for the entire space must lead to systematic errors in the calculated
distances reaching 10%. 相似文献
13.
The young open star cluster M25 (IC 4725) is located in the direction of the galactic center, near much irregular absorption
features on Sagittarius arm. This system is found to be at a distance of 600 pc, with a median age of 9.45 × 107 years and a distance from the galactic plane of –52.82 pc The mass data available in the literature has been gathered and
many statistical methods have been applied for this cluster. Depending only on these methods, the stellar density, the distribution
of dark matter, the luminosity and the mass functions have been estimated. The center of the cluster has been defined, it
is shifted by 45 arc sec in the northeast direction. The radius of the cluster is found to be 4 pc. More than 220 stars with
mean reddening of 0.50 mag and absorption of 1.62mag are found inside this aria. The total mass of the cluster has been estimated
with the mass of the interstellar matter (gas and dust). It is found to be 1937 M
⊙, whereas about 24% of the material mass of the cluster has remained as interstellar matter after the processes of formation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Photoelectric Vilnius photometry of the B-type stars HD 29 647 and HDE 283 809 in the direction of the Taurus molecular cloud indicates their brightness and energy distribution to be constant within 1–2%. The interstellar extinction law is determined for the star HDE 283 809 from the photometry data in the Vilnius andUBVRJHKL systems, which yield the ratioR=A
V/EB-V=3.5 and grain sizes exceeding the average by approximately 10%. The interstellar extinction law for the two stars is found to be the same in the infrared, however, it is very different in the near ultraviolet. The new spectra of HDE 283 809 confirm the earlier classification and indicate an absence of emission in the hydrogen lines. The interstellar band at 443 nm is observed but its intensity is a half of what is expected forE
B-V=1.61. The observed peculiarities of the energy distribution in the spectrum of HDE 283 809 apparently originate in interstellar or circumstellar dust, not in the star itself.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
15.
Interstellar and atmospheric extinctions redden the observational photometric data and they should be handled rigorously.
This paper simulates the effect of reddening for the modest case of two main sequence T
1 = 6500 K and T
2 = 5500 K components of a detached eclipsing binary system. It is shown that simply subtracting a constant from measured magnitudes
(the approach often used in the field of eclipsing binaries) to account for reddening should be avoided. Simplified treatment
of the reddening introduces systematics that reaches ∼0.01 mag for the simulated case, but can be as high as ∼0.2 mag for,
e.g., B8 V-K4 III systems. With rigorous treatment, it is possible to uniquely determine the colour excess value E(B−V) from multi-colour photometric light curves of eclipsing binaries. 相似文献
16.
G. A. Gontcharov 《Astronomy Letters》2009,35(9):638-650
The stellar composition of the Tycho-2 Catalogue in the range B-V = 0·
m
75–1·
m
25 has been reproduced through Monte Carlo simulations. For young and old stars of the red giant clump (RGC), the red giant
branch, subgiants, red dwarfs, and thick-disk giants, we have specified the distributions in coordinates, velocities, B-V, and M
V
as a function of B-V and calculated their reduced proper motions, photometric distances from the (B-V)-M
V
calibration, and photoastrometric distances from the reduced proper motion-M
V
calibration. Our simulations have shown the following: (1) a sample of thin-disk giants within 500 pc with an admixture of
less than 10% of other stars can be produced; (2) a sample of dwarfs within 100 pc almost without any admixture of other stars
can be produced; (3) the Local Spiral Arm affects the RGC composition of any magnitude-limited catalog in favor of giants
younger than 2 Gyr; (4) the samples produced using reduced proper motions can be used for kinematic studies, provided that
the biases of the quantities being determined are simulated and taken into account; (5) the photometric distances correlate
with the photoastrometric ones because of the correlation between the proper motion and magnitude; (6) the photometric distances
are closer to the true ones for the red giant branch and red dwarfs as the categories of stars with a clear (B-V)-M
V
relation, while the photoastrometric distances are closer to the true ones for the RGC, subgiants, and thick-disk giants;
(7) the calculated distances differ systematically from the true ones, but they can be used to analyze the three-dimensional
distribution of stars. Our simulations confirm the validity of our previous selection of RGC stars from Tycho-2. 相似文献
17.
F. Zagury 《Astronomische Nachrichten》2013,334(10):1107-1114
The 2200 Å bump is a major figure of interstellar extinction. However, extinction curves with no bump exist and are, with no exception, linear from the near‐infrared down to 2500 Å at least, often over all the visible‐UV spectrum. The duality linear versus bump‐like extinction curves can be used to re‐investigate the relationship between the bump and the continuum of interstellar extinction, and answer questions as why do we observe two different kinds of extinction (linear or with a bump) in interstellar clouds? How are they related? How does the existence of two different extinction laws fits with the requirement that extinction curves depend exclusively on the reddening E (B – V) and on a single additional parameter? What is this free parameter? It will be found that (1) interstellar dust models, which suppose the existence of three different types of particles, each contributing to the extinction in a specific wavelength range, fail to account for the observations; (2) the 2200 Å bump is very unlikely to be absorption by some yet unidentified molecule; (3) the true law of interstellar extinction must be linear from the visible to the far‐UV, and is the same for all directions including other galaxies (as the Magellanic Clouds). In extinction curves with a bump the excess of starlight (or the lack of extinction) observed at wavelengths less than λ = 4000 Å arises from a large contribution of light scattered by hydrogen on the line of sight. Although counter‐intuitive this contribution is predicted by theory. The free parameter of interstellar extinction is related to distances between the observer, the cloud on the line of sight, and the star behind it (the parameter is likely to be the ratio of the distances from the cloud to the star and to the observer). The continuum of the extinction curve and the bump contain no information on the chemical composition of interstellar clouds. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
Arūnas Kučinskas Audrius Bridžius Vladas Vansevičius 《Astrophysics and Space Science》2002,280(1-2):159-163
The goal of this work is to assess the expected scientific output from the photometric studies of globular clusters in the
Large Magellanic Cloud with ESA's astrometric space mission GAIA. For this purpose we simulate GAIA photometry of individual
stars in synthetic cluster populations, covering a large range of cluster ages and metallicities. We find that accurate effective
temperatures (Δ T
eff<10%) can be obtained from GAIA photometry down to V ∼ 18 for stars in populations within the studied metallicity range ([M/H] = -0.4 ... -1.7). GAIA will also provide photometric
metallicities (Δ [M/H] ≲ 0.3 dex) for the cluster giants brighter than V ∼ 17.5. The knowledge of the effective temperature sand metallicities will allow to obtain accurate ages of stellar populations
younger than about 1 Gyr using the usual procedure of main sequence turn-off point fitting. Ages of older stellar populations
(≳ 1 Gyr) may be constrained from the isochrone fits to the giant branches in the observed CMDs. We conclude that GAIA will
provide excellent opportunities for studying star formation histories far beyond the Milky Way, providing means for better
understanding of stellar and galactic evolution in different astrophysical environments.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
High resolution observations of interstellar Na Iabsorptions in the spectra of early-type stars in the second Galacticquadrant have been used to derive the spatial distribution of thenearby interstellar gas in the Galactic anticentre hemisphere. The datashow the presence, within the region explored and within the nearest150 pc, of eight diffuse interstellar clouds with LSR velocities in therange 15–55 km s-1. Molecular gas previously identified close tothe Sun by Trapero et al. (1995) and Trapero et al. (1996) is embeddedin one of the clouds. The motion of these clouds does not reflect anymotion of the gas away from the Scorpio-Centaurus association, showingthat the kinematics observed in the neighbourhood of the Sun byLallement and Bertin (1992) is restricted, in the second Galactic quadrant,to the nearest 50 pc. 相似文献
20.
We present the results of a search for carbon recombination lines in the Galaxy at 34.5 MHz (C575α) made using the dipole
array at Gauribidanur near Bangalore. Observations made towards 32 directions resulted in detections of lines, in absorption
at nine positions. Followup observations at 328 MHz (C272α) using the Ooty Radio Telescope detected these lines in emission.
A VLA D-array observation of one of the positions at 330 MHz yielded no detection implying a lower limit of 10′ for the angular
size of the line forming region.
The longitude-velocity distribution of the observed carbon lines indicate that the line forming regions are located mainly
between 4 kpc and 7 kpc from the Galactic centre. Combining our results with published carbon recombination line data near
76 MHz (Erickson, McConnell & Anantharamaiah 1995), we obtain constraintson the physical parameters of the line forming regions.
We find thatif the angular size of the line forming regions is ≥ 4°, then the range of parameters that fit the data are:T
e
=20–40 K,n
e
∼ 0.1–0.3 cm−3 and pathlengths ∼ 0.07–0.9 pc which may correspond to thin photodissociated regions around molecular clouds. On the other
hand, if the line forming regions are ∼ 2° in extent, then warmer gas (T
e
∼ 60–300 K) with lower electron densities (n
e
∼ 0.03–0.05 cm−3) extending over several tens of parsecs along the line of sight and possibly associated with atomic HI gas can fit the data.
Based on the range of derived parameters, we suggest that the carbon line regions are most likely associated with photo-dissociation
regions. 相似文献