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1.
The peculiar galaxy NGC 4650 A (α=12h 42m. 1; = δ—40° 26′; 1950·0) has been studied by means of direct and spectral observations with the ESO 3·6-m telescope. It is
interpreted as a prolate, elliptical galaxy surrounded by a warped ring of H II regions, dust and stars. The distance is 47
Mpc (H
0=55 km s−1 Mpc−1). The ring is seen nearly edge-on (inclination 85°) and it rotates. It has a diameter of about 21 kpc and is bluer than the
elliptical galaxy for which the (M/L
v) ratio is ∼12 in solar units. The observed configuration may be the result of interaction with the nearby galaxy, NGC 4650. 相似文献
2.
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
3.
P. Amram C. Mendes de Oliveira H. Plana C. Balkowski M. Bolte 《Astrophysics and Space Science》2002,281(1-2):397-400
We present kinematics and photometric evidence for the presence of seven candidate tidal dwarf galaxies in Stephan's Quintet.
The central regions of the two most probable parent galaxies, NGC 7319 and NGC 7318B, contain little or no gas whereas the
intragroup medium and, in particular, the optical tails that seem to be associated with NGC 7318B are rich in cold and ionized
gas. Two tidal dwarf candidates may be located at the edge of a tidal tail, another located within a tail, and for the four
others there is no obvious stellar/gaseous bridge between them and the parent galaxy. Two of the candidates are associated
with H I clouds, one of which is, in addition, associated with a CO cloud. All seven regions have low continuum fluxes and
high Hα luminosity densities [F(Hα) = (1-60) × 10-14 ergs s-1 cm-2]. Their magnitudes (MB = –16.1 to –12.6), sizes (∼ 3.5 h75
-1 kpc), colors (typically B – R = 0.7), and gas velocity gradients (∼ 8 –26 h75 km s-1 kpc-1) are typical for tidal dwarf galaxies. In addition, the ratios between their star formation rates determined from Hα and
from the B-band luminosity are typical of other tidal dwarf galaxies. The masses of the tidal dwarf galaxies in Stephan's
Quintet range from ∼ 2 × 108 to 1010 M⊙, and the median value for their inferred mass-to-light ratios is 7 (M/L)⊙. At least two of the systems may survive possible ‘fallbacks’ or disruption by the parent galaxies and may already be, or
turn into, self-gravitating dwarf galaxies, new members of the group.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
4.
S. Bilir T. Güver I. Khamitov T. Ak S. Ak K. B. Coşkunoğlu E. Paunzen E. Yaz 《Astrophysics and Space Science》2010,326(1):139-150
We present CCD BV and JHK
s
2MASS photometric data for the open cluster NGC 1513. We observed 609 stars in the direction of the cluster up to a limiting
magnitude of V∼19 mag. The star-count method showed that the centre of the cluster lies at α
2000=04
h
09
m
36
s
, δ
2000=49°28′43″ and its angular size is r=10 arcmin. The optical and near-infrared two-colour diagrams revealed the colour excesses in the direction of the cluster
as E(B−V)=0.68±0.06, E(J−H)=0.21±0.02 and E(J−K
s
)=0.33±0.04 mag. These results are consistent with normal interstellar extinction values. Optical and near-infrared Zero Age
Main-Sequences (ZAMS) provided an average distance modulus of (m−M)0=10.80±0.13 mag, which can be translated into a distance of 1440±80 pc. Finally, using Padova isochrones we determined the
metallicity and age of the cluster as Z=0.015±0.004 ([M/H]=−0.10±0.10 dex) and log (t/yr)=8.40±0.04, respectively. 相似文献
5.
Rekhesh Mohan K. S. Dwarakanath G. Srinivasan 《Journal of Astrophysics and Astronomy》2004,25(3-4):185-201
We have carried out a sensitive high-latitude (|b| > 15°) HI 21 cm-line absorption survey towards 102 sources using the GMRT. With a 3σ detection limit in optical depth of
∼ 0.01, this is the most sensitive HI absorption survey. We detected 126 absorption features most of which also have corresponding
HI emission features in the Leiden Dwingeloo Survey of Galactic neutral Hydrogen. The histogram of random velocities of the
absorption features is well-fit by two Gaussians centered at V1sr ∼ 0 km s−1 with velocity dispersions of 7.6 ± 0.3 km s−1 and 21 ± 4 km s−1 respectively. About 20% of the HI absorption features form the larger velocity dispersion component. The HI absorption features
forming the narrow Gaussian have a mean optical depth of 0.20 ± 0.19, a mean HI column density of (1.46 ± 1.03) × 1020 cm−2, and a mean spin temperature of 121 ± 69 K. These HI concentrations can be identified with the standard HI clouds in the
cold neutral medium of the Galaxy. The HI absorption features forming the wider Gaussian have a mean optical depth of 0.04
± 0.02, a mean HI column density of (4.3 ± 3.4) × 1019 cm−2, and a mean spin temperature of 125 ± 82 K. The HI column densities of these fast clouds decrease with their increasing random
velocities. These fast clouds can be identified with a population of clouds detected so far only in optical absorption and
in HI emission lines with a similar velocity dispersion. This population of fast clouds is likely to be in the lower Galactic
Halo. 相似文献
6.
This is an account of Allan Sandage’s work on (1) The character of the expansion field. For many years he has been the strongest defender of an expanding Universe. He later explained the CMB dipole by a local velocity of 220±50 km s−1 toward the Virgo cluster and by a bulk motion of the Local supercluster (extending out to ∼3500 km s−1) of 450–500 km s−1 toward an apex at l=275, b=12. Allowing for these streaming velocities he found linear expansion to hold down to local scales (∼300 km s−1). (2) The calibration of the Hubble constant. Probing different methods he finally adopted—from Cepheid-calibrated SNe Ia and from independent RR Lyr-calibrated TRGBs—H 0=62.3±1.3±5.0 km s−1 Mpc−1. 相似文献
7.
M. Yu. Piotrovich Yu. N. Gnedin T. M. Natsvlishvili N. A. Silant’ev 《Astronomy Letters》2010,36(6):389-395
We analyze the spectropolarimetric observations of 12 candidates for quasars from the spectroscopic database of the SDSS Catalog.
The magnetic fields of these objects are estimated in the context of a theory that includes the Faraday rotation of the polarization
plane on the mean free path of a photon in the outflow from an accretion disk. As a result, we have determined the column
density in the outflow, N
H ∼ 6 × 1023 cm−2, and the radial, B ∼ 1 G, and toroidal, B ∼ 600 G, magnetic fields. 相似文献
8.
E. Sánchez-Ayaso J. A. Combi J. F. Albacete Colombo J. López-Santiago J. Martí A. J. Mu?oz-Arjonilla 《Astrophysics and Space Science》2012,337(2):573-579
We report XMM-Newton observations of the Galactic supernova remnant G296.8-0.3, together with complementary radio and infrared data. The spatial
and spectral properties of the X-ray emission, detected towards G296.8-0.3, was investigated in order to explore the possible
evolutionary scenarios and the physical connexion with its unusual morphology detected at radio frequencies. G296.8-0.3 displays
diffuse X-ray emission correlated with the peculiar radio morphology detected in the interior of the remnant and with the
shell-like radio structure observed to the northwest side of the object. The X-ray emission peaks in the soft/medium energy
range (0.5–3.0 keV). The X-ray spectral analysis confirms that the column density is high (N
H∼0.64×1022 cm−2) which supports a distant location (d>9 kpc) for the SNR. Its X-ray spectrum can be well represented by a thermal (PSHOCK) model, with kT∼0.86 keV, an ionization timescale of 6.1×1010 cm−3 s, and low abundance (∼0.12 Z
⊙). The 24 μm observations show shell-like emission correlated with part of the northwest and southeast boundaries of the SNR.
In addition a point-like X-ray source is also detected close to the geometrical center of the radio SNR. The object presents
some characteristics of the so-called compact central objects (CCO). Its X-ray spectrum is consistent with those found at
other CCOs and the value of N
H is consistent with that of G296.8-0.3, which suggests a physical connexion with the SNR. 相似文献
9.
A new orbital period analysis for U Geminorum is made by means of the standard O–C technique based on 187 times of light minima
including the three newest CCD data from our observation. Although there are large scatter near 70,000 cycles in its O–C diagram,
there is strong evidence (>99.9% confidence level) to show the secular increase of orbital period with a rate
s−1. Using the physical parameters recently derived by Echevarría et al. (Astron. J. 134:262, 2007), the range of mass transfer rate for U Geminorum is estimated as from −3.5(5)×10−9 M
⊙ yr−1 to −1.30(6)×10−8 M
⊙ yr−1. Moreover, the data before 60,000 cycles shows the obvious quasi-period variations. The least square estimation of a ∼17.4 yr
quasi-periodic variation superimposed on secular orbital period increase is derived. Considering the possibility that solar-type
magnetic activity cycles in the secondary star of U Geminorum may produce the quasi-period variations of the orbital period,
Applegate’s mechanism is discussed and the results indicate such mechanism has difficulty explaining the quasi-period variation
for U Geminorum. Hence, we attempted to apply the light-travel time effect to interpret the quasi-period variation and found
the perturbation of ∼17.4 yr quasi-period may result from a brown dwarf. If the orbital inclination is assumed as i∼15°, corresponding to the upper limit of mass of a brown dwarf, then its orbital radii is ∼7.7 AU. 相似文献
10.
We present the results of our infrared observations of WR 140 (=V1687 Cyg) in 2001–2010. Analysis of the observations has
shown that the J brightness at maximum increased near the periastron by about 0
m
.3; the M brightness increased by ∼2
m
in less than 50 days. The minimum J brightness and the minimum L and M brightnesses were observed 550–600 and 1300–1400 days after the maximum, respectively. The JHKLM brightness minimum was observed in the range of orbital phases 0.7–0.9. The parameters of the primary O5 component of the
binary have been estimated to be the following: R(O5) ≈ 24.7R
⊙, L(O5) ≈ 8 × 105
L
⊙, and M
bol(O5) ≈ −10
m
. At the infrared brightness minimum, T
g ∼ 820–880 K, R
g ≈ 2.6 × 105
R
⊙, the optical depth of the shell at 3.5 μm is ∼5.3 × 10−6, and its mass is ≈1.4 × 10−8
M
⊙. At the maximum, the corresponding parameters are ∼1300 K, 8.6 × 104
R
⊙, ∼2 × 10−4, and ∼6 × 10−8
M
⊙; the mean rate of dust inflow (condensation) into the dust structure is ∼3.3 × 10−8
M
⊙ yr−1. The mean escape velocity of the shell from the heating source is ∼103 km s−1 and the mean dispersal rate of the shell is ∼1.1 × 10−8
M
⊙ yr−1. 相似文献
11.
R. Ruiterkamp S. B. Charnley H. M. Butner H.-C. Huang S. D. Rodgers Y.-J. Kuan P. Ehrenfreund 《Astrophysics and Space Science》2007,310(3-4):181-188
We have observed emission from both ortho and para spin states of ketene (CH2CO) towards several deeply-embedded protostars. The low CH2CO fractional abundances (∼10−10) and the rotation temperatures (∼20 K) are consistent with emission from the cooler envelope. We compare our results with
previous studies and discuss possible production pathways to interstellar ketene. We suggest that, if low observed excitation
temperatures of CH2CO, CH3CHO and H2CO are indicative of their absence from the hot core region, then this may be due to the extensive hydrogenation of pre-existing
grain mantles prior to evaporation into the inner envelope, leading to lower abundances of these compounds and to mantles
rich in alcohols. 相似文献
12.
V. N. Frolov Yu. K. Ananjevskaja D. L. Gorshanov E. V. Polyakov 《Astronomy Letters》2010,36(5):338-348
We present the results of our comprehensive study of the Galactic open star cluster NGC 6866. The positions of stars in the
investigated region have been obtained with the “Fantasy” automatic measuring machine from 10 plates of the normal astrograph
at the Pulkovo Astronomical Observatory. The size of the investigated field is 40′ × 40′, the limiting magnitude is B ∼ 16·
m
6, and the maximum epoch difference is 79 yr. For 1202 field stars, we have determined the relative proper motions with an
rms error of 2.5 mas yr−1. Out of them, 423 stars may be considered cluster members with a probability P > 70% according to the astrometric criterion. Photometric diagrams have been used as an additional criterion. We have performed
two-color BV CCD photometry of stars with the Pulkovo ZA-320M mirror astrograph. The U magnitudes from the literature have also been used to construct the two-color diagrams. A total of 267 stars have turned
out to be members of NGC 6866 according to the two criteria. We present refined physical parameters of the cluster and its
age estimate (5.6 × 108 yr). The cluster membership of red and blue giants, variable, double, and multiple stars is considered. We have found an
almost complete coincidence of the positions of one of the stars in the region (a cluster nonmember) and a soft X-ray source
in the ROSAT catalog. The “Fantasy” automatic measuring machine is described in the Appendix. 相似文献
13.
D. Reynaud 《Astrophysics and Space Science》2001,276(2-4):619-624
Bars probably have a great importance in galactic evolution. The barred potential is able to concentrate large quantities
of interstellar gas in the vicinity of the nucleus, feeding any nuclear activity, be it central starbursts or black hole accretion
discs. The IRAM millimeter interferometer and 30 m telescope have allowed a precise analysis of the molecular gas in the bar
and the nucleus of a typical barred spiral galaxy, NGC 1530. In this galaxy, I have detected CO(1→0) along two lanes that
trace shocks in the molecular gas. In these lanes, the gas moves toward the centre of the galaxy, with typical in fall velocities
of 100 km s-1. I have shown in these shocks an anticorrelation between shear in the gas and star formation efficiency by comparing Hα and CO maps. I have also studied the centre of this galaxy at higher resolution in12CO(1→0), 12CO(2→1),13CO(1→0) and HCN(1→0). In the central region, the gas distribution is a ring or an unresolved spiral, surrounded by two curved
arcs. The nuclear ring contains large amounts of dense gas traced by HCN and 13CO, and shows intense star formation, as indicated by the non-thermal centimetre continuum. The arcs, in contrast, are poor
in dense gas and form few stars.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Optical CCD imaging with Hα and [SII] filters and spectroscopic observations of the galactic supernova remnant G85.9-0.6 have been performed for the
first time. The CCD image data are taken with the 1.5 m Russian-Turkish Telescope (RTT150) at TüBİTAK National Observatory
(TUG) and spectral data are taken with the Bok 2.3 m telescope on Kitt Peak, AZ.
The images are taken with narrow-band interference filters Hα, [SII] and their continuum. [SII]/Hα ratio image is performed. The ratio obtained from [SII]/Hα is found to be ∼0.42, indicating that the remnant interacts with HII regions. G85.9-0.6 shows diffuse-shell morphology. [SII]λ
λ6716/6731 average flux ratio is calculated from the spectra, and the electron density N
e
is obtained to be 395 cm−3. From [OIII]/Hβ ratio, shock velocity has been estimated, pre-shock density of n
c
=14 cm−3, explosion energy of E=9.2×1050 ergs, interstellar extinction of E(B−V)=0.28, and neutral hydrogen column density of N(HI)=1.53×1021 cm−2 are reported. 相似文献
15.
Alessandro Boselli James Lequeux Giuseppe Gavazzi 《Astrophysics and Space Science》2002,281(1-2):127-128
The molecular gas mass in nearby galaxies is generally estimated using 12CO(1-0) line intensities and assuming the X conversion factor between I(CO) and N(H2) measured in the solar neighborhood. It is however known that this X conversion factor is not universal since it changes with metallicity, cosmic ray density and UV radiation field. Far-IR data
in the spectral range 100-1000 μm can be used to estimate the molecular gas content of late-type galaxies in an independent
way of CO line measurements once a metallicity-dependent dust to gas ratio is assumed, allowing a direct estimate of X. This exercise is presented here for a large sample of galaxies with available multifrequency data. X spans from ∼ 1020 mol cm-2 (K km s-1)-1 in giant spirals to ∼ 1021 mol cm-2 (K km s-1)-1 in dwarf irregulars.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
16.
The collisional pumping of H216O and H218O masers in hot dense gas-dust clouds has been simulated numerically. New data on the rate coefficients for collisional transitions
from Faure et al. (2007) were used in the calculations. The possibility of detecting H218O emission in 22.2-GHz H216O maser sources is investigated. The medium is shown to become optically thick in the H218O lines for which an inverted level population is observed at H2O column densities of ∼1019–1020 cm−2. A simultaneous observation of H218O emission and H216O maser emission in the same source will allow the physical conditions in the gas-dust cloud to be refined. 相似文献
17.
We present new radio observations of molecular lines in the region of high mass star formation, namely G122.0-7.1. A large-scale
map of the emission observed in the 12CO (J = 1−0) and 13CO (J = 1−0) lines covers the area of 15′ × 9′, revealing two dense regions. The molecular bipolar outflows have been resolved
in ASO1 region. It is associated with the known candidate YSO nearby IRAS 0042 + 5530. Also, a new dense region has been discovered
in the North-Western part of the G122.0-7.1 at a distance of 5′ from IRAS 0042 + 5530. Its position is close to the peak of
4850 MHz emission.
The text was submitted by the authors in English. 相似文献
18.
We present the first CCD photometric UBVRI observations of the not-so-well-studied open cluster NGC 1624 (OCl 403, Cr 53; α2000 = 04 h 40 m 36 s; δ2000 = + 50˚ 27′ 42″ Trumpler class = I 2 p N). This cluster was observed on 01 February 2004 with the 2 m Himalayan Chandra Telescope at Hanle using a LN2 cooled 2k × 2k CCD. The cluster presents differential reddening with E(B-V) values ranging from 0.70 to 0.90 mag, which could be attributed to the presence of the HII region wherein the cluster is embedded. It is found to be at a distance of 6.025 ± 0.5 kpc and the age of this cluster is estimated to be ∼3.98 × 106 years. In view of these parameters, it can be considered as a young enough cluster located in the direction of the Perseus constellation with the galactic coordinates of l = 155˚.35 and b = + 02 ˚.58. Thus it could also be used as a suitable candidate for tracing the Outer Perseus spiral arm of our Galaxy. The initial mass function slope is derived as 1.65 ± 0.25 by applying the corrections for field star contamination and data incompleteness. This is in good agreement with the Salpeter value within the limits of errors. 相似文献
19.
K. S. Dwarakanath Siddharth Malu Ruta Kale 《Journal of Astrophysics and Astronomy》2011,32(4):529-532
We have discovered a giant radio halo in the massive merging cluster MACSJ0417.5-1154. This cluster, at a redshift of 0.443,
is one of the most X-ray luminous galaxy cluster in the MAssive Cluster Survey (MACS) with an X-ray luminosity in the 0.1–2.4
keV band of 2.9×1045 erg s − 1. Recent observations from GMRT at 230 and 610 MHz have revealed a radio halo of ∼ 1.2 × 0.3 Mpc2 in extent. This halo is elongated along the North-West, similar to the morphology of the X-ray emission from Chandra. The
1400 MHz radio luminosity (L
r) of the halo is ∼2 × 1025 W Hz − 1, in good agreement with the value expected from the L
x − L
r correlation for cluster halos. 相似文献
20.
V. I. Shematovich 《Solar System Research》2010,44(2):96-103
The ionization and dissociation of molecular hydrogen by the ultraviolet (UV) radiation of the parent star lead to the formation
of hydrogen atoms with an excess of kinetic energy and, thus, are an important source of suprathermal hydrogen atoms in the
upper atmosphere of exoplanet HD 209458b. Contemporary aeronomical models did not investigate these processes because they
assumed the fast local thermalization of the hot atoms of hydrogen by elastic collisions. However, the kinetics and transfer
of these atoms were not calculated in detail, because they require the solving of the Boltzmann equation for a nonthermal
atom population. This work estimates the effect of the UV radiation of the parent star and the accompanying photocleacton
flux on the production of the suprathermal fraction of atomic hydrogen in the H2 → H transition region. We also consider the formation of the escaping flux of Hatoms created by this effect in the upper
atmosphere of HD 209458b. We calculate the production rate and energy spectrum of the hydrogen atoms with excess kinetic energy
during the dissociation of H2. Using the numerical stochastic model created by Shematovich (2004) for a hot planetary corona, we investigate the molecular-scale
kinetics and transfer of suprathermal hydrogen atoms in the upper atmosphere and the emergent flux of atoms evaporating from
the atmosphere. The latter is estimated as 3.4 × 1012 cm−2 s−1 for a moderate stellar activity level of UV radiation, which leads to a planetary atmosphere evaporation rate of 3.4 × 109 g s−1 due to the process of the dissociation of H2. This estimate is close to the observational value of ∼1010 g s−1 for the rate of atmospheric loss of HD 209458b. 相似文献