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1.
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
2.
Any calibration of the present value of the Hubble constant (H
0) requires recession velocities and distances of galaxies. While the conversion of observed velocities into true recession
velocities has only a small effect on the result, the derivation of unbiased distances which rest on a solid zero point and
cover a useful range of about 4–30 Mpc is crucial. A list of 279 such galaxy distances within v < 2,000 km s−1 is given which are derived from the tip of the red-giant branch (TRGB), from Cepheids, and/or from supernovae of type Ia
(SNe Ia). Their random errors are not more than 0.15 mag as shown by intercomparison. They trace a linear expansion field
within narrow margins, supported also by external evidence, from v = 250 to at least 2,000 km s−1. Additional 62 distant SNe Ia confirm the linearity to at least 20,000 km s−1. The dispersion about the Hubble line is dominated by random peculiar velocities, amounting locally to <100 km s−1 but increasing outwards. Due to the linearity of the expansion field the Hubble constant H
0 can be found at any distance >4.5 Mpc. RR Lyr star-calibrated TRGB distances of 78 galaxies above this limit give H
0 = 63.0 ± 1.6 at an effective distance of 6 Mpc. They compensate the effect of peculiar motions by their large number. Support
for this result comes from 28 independently calibrated Cepheids that give H
0 = 63.4 ± 1.7 at 15 Mpc. This agrees also with the large-scale value of H
0 = 61.2 ± 0.5 from the distant, Cepheid-calibrated SNe Ia. A mean value of H
0 = 62.3 ± 1.3 is adopted. Because the value depends on two independent zero points of the distance scale its systematic error
is estimated to be 6%. Other determinations of H
0 are discussed. They either conform with the quoted value (e.g. line width data of spirals or the D
n
−σ method of E galaxies) or are judged to be inconclusive. Typical errors of H
0 come from the use of a universal, yet unjustified P–L relation of Cepheids, the neglect of selection bias in magnitude-limited
samples, or they are inherent to the adopted models. 相似文献
3.
A. é. Rosenbush 《Astrophysics》1999,42(4):425-430
It is proposed to interpret the outbursts of Nova Aquilae 1919 (V605 Aql) and the nova-like outburst of Sakurai’s object in
1996 as recurrent outbursts of classical novae of the DQ Her and RR Pic types with recurrence periods of about 1100 and 50,000
years, respectively, and some characteristics of these stars are derived on that basis. Only now has V605 Aql returned to
the quiet state, and it has an absolute visual magnitude no fainter than 8m−9m. The orbital inclination of the prenova’s binary system is about 90°. The absolute visual magnitude of the prenova of V4334
Sgr is no brighter than 3m. It is quite possible that the orbital inclination of the prenova’s binary system is close to 0°. The expansion velocities
of the shells are 30–40 km/sec in both cases. The structure of the ejection is conserved in the recurrent outbursts.
Translated from Astrofizika, Vol. 42, No. 4, pp. 563–570, October–December, 1999. 相似文献
4.
Michael J. Price 《Icarus》1973,20(4):455-464
New measurements of the equivalent widths of the 4-0 S(0) and S(1) H2 quadrupole lines in the Uranian spectrum have been obtained using high dispersion (4.12 Å/mm) image-tube spectrography. The measured equivalent widths are for the S(0) and S(1) lines, respectively. Curve-of-growth analysis in terms of a reflecting layer model yields an H2 column-density of 780?330+940km amagat and a temperature of 78?24+80°K. Interpretation using a semi-infinite, homogeneous, isotropically scattering model for line formation yields a scattering mean free path at λ6400 Å of 550 ± 250 km amagat. Quoted errors for both the H2 column-density and the scattering mean free path include the effect of uncertainty in the choice of atmospheric temperature. The results are discussed in terms of current models for the Uranian atmosphere. 相似文献
5.
Burša Milan Kenyon Steve Kouba Jan Müller Achim Raděj Karel Vatrt Viliam Vojtíšková Marie Vítek Vojtěch 《Earth, Moon, and Planets》1999,84(3):163-176
The TOPEX/POSEIDON (T/P) satellite altimeter data from January 1, 1993to October 24, 1999 (cycles 11–261) was used for investigating
thelong-term variations in the geoidal geopotential W0 and/orin the geopotential scale factor R0 = GM/W0 (GM is theadopted geocentric gravitational constant). The mean valuesdetermined for the whole period covered are: W0 =(62 636 856.161 ± 0.002) m2 s-2, R0 =(6 363 672.5448 ± 0.0002) m. The actual accuracy is limited bythe altimeter calibration error (2–3 cm) and it isestimated
to be about ± 0.5 m2 s-2 (± 5 cm).The yearly variations of the above mean values are at the formalerror level. No long-term trend in W0, representing the oceanvolume change, was found for the seven years period 1993–9 on thebasis of T/P altimeter (AVISO) data.
No sea surface topography modelwas used in the solution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
To study the peculiarities of the Galactic spiral density wave, we have analyzed the space velocities of Galactic Cepheids with propermotions from the Hipparcos catalog and line-of-sight velocities from various sources. First, based on the entire sample of 185 stars and taking R 0 = 8 kpc, we have found the components of the peculiar solar velocity (u ⊙, v ⊙) = (7.6, 11.6) ± (0.8, 1.1) km s?1, the angular velocity of Galactic rotation Ω0 = 27.5 ± 0.5 km s?1 kpc?1 and its derivatives Ω′0 = ?4.12 ± 0.10 km s?1 kpc?2 and Ω″0 = 0.85 ± 0.07 km s?1 kpc?3, the amplitudes of the velocity perturbations in the spiral density wave f R = ?6.8 ± 0.7 and f θ = 3.3 ± 0.5 km s?1, the pitch angle of a two-armed spiral pattern (m = 2) i = ?4.6° ± 0.1° (which corresponds to a wavelength λ = 2.0 ± 0.1 kpc), and the phase of the Sun in the spiral density wave χ⊙ = ?193° ± 5°. The phase χ⊙ has been found to change noticeably with the mean age of the sample. Having analyzed these phase shifts, we have determined the mean value of the angular velocity difference Ω p ? Ω, which depends significantly on the calibrations used to estimate the individual ages of Cepheids. When estimating the ages of Cepheids based on Efremov’s calibration, we have found |Ω p ? Ω0| = 10 ± 1stat ± 3syst km s?1 kpc?1. The ratio of the radial component of the gravitational force produced by the spiral arms to the total gravitational force of the Galaxy has been estimated to be f r0 = 0.04 ± 0.01. 相似文献
7.
Douglas S. Hall Gregory W. Henry Dietmar Böhme Peter A. Brooks Sandy Chang Ales Dolzan George L. Fortier Robert E. Fried Russell M. Genet Bruce S. Grim James Hannon Darrel B. Hoff Kevin Krisciunas Howard J. Landis Howard P. Louth Larry P. Lovell Paul Nielsen Bobby E. Powell Harry D. Powell Don Pray Thomas R. Renner Charles W. Rogers Stephen Shervais Douglas M. Slauson Samuel Slote Harold J. Stelzer Arthur J. Stokes Jack C. Troeger Louis C. Turner Norman F. Wasson Kenneth W. Zeigler 《Journal of Astrophysics and Astronomy》1991,12(4):281-287
We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29
different observatories. Then we combine it with all other photometry available to us (previously published, contained in
the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to
yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season,
we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0m.09 down almost to 0m.03. The spot rotation periods were 55d.9 ± 0d.6 and 520d.8 ± 1d.0, respectively. 相似文献
8.
Yu. N. Kudrya V. E. Karachentseva I. D. Karachentsev S. N. Mitronova W. K. Huchtmeier 《Astronomy Letters》2006,32(2):73-83
We analyze the peculiar velocity field for 2400 flat spiral galaxies selected from an infrared sky survey (2MFGC). The distances to the galaxies have been determined from the Tully-Fisher relation in the photometric J band with a dispersion of 0m.45. The bulk motion of this sample relative to the cosmic microwave background (3K) frame has an amplitude of 199 ± 37 km s?1 in the direction l = 290° ± 11°, b = +1° ± 9°. The amplitude of the dipole motion tends to decrease with distance in accordance with the expected convergence of bulk flows in the 3K frame. We believe that external massive attractors similar to the Shapley cluster concentration are responsible for ~60% of the local flow velocity in the z = 0.03 volume. 相似文献
9.
The Tully–Fisher relationship (TFR) has been shown to have a relatively small observed scatter of ∼±0.35 mag implying an intrinsic
scatter < ±0.30 mag. However, when the TFR is calibrated from distances derived from the Hubble relation for field galaxies
scatter is consistently found to be ±0.64 to ±0.84 mag. This significantly larger scatter requires that intrinsic TFR scatter
is actually much larger than ±0.30 mag, that field galaxies have an intrinsic TFR scatter much larger than cluster spirals,
or that field galaxies have a velocity dispersion relative to the Hubble flow in excess of 1000 km s−1. Each of these potential explanations faces difficulties and contradicted by available data and the results of previous studies.
An alternative explanation is that the measured redshifts of galaxies are composed of a cosmological redshift component predicted
from the value of the Hubble constant and a superimposed intrinsic redshift component previously identified in other studies.
This intrinsic redshift component may exceed 5000 km s−1 in individual galaxies. In this alternative scenario a possible value for the Hubble constant is 55–60 km s−1 Mpc−1. 相似文献
10.
Shiro Nishimura 《Astrophysics and Space Science》1969,3(1):77-79
The metallic-line A-type star 28 And was found to be variable both in brightness and radial velocity. The brightness in blue varies by 0m.05, and the radial velocity by 5 km/sec with a period of 102 minutes. The minimum light occurs 0.12 P before the maximum radial velocity. The relation of 28 And to Scuti variables is briefly discussed. 相似文献
11.
Based on currently available observations of 28 maser sources in 25 star-forming regions with measured trigonometric parallaxes,
proper motions, and radial velocities, we have constructed the rotation curve of the Galaxy. Taking different distances to
the Galactic center R
0, we have estimated the peculiar velocity of the Sun, the angular velocity of Galactic rotation, and its three derivatives.
For R
0 = 8 kpc, we have found the circular velocity of the Sun to be V
0 = 243 ± 16 km s−1, which corresponds to a revolution period of 202 ± 10 Myr. We have obtained the Oort constants A = 16.9 ± 1.2 km s−1 kpc−1 and B = −13.5 ± 1.4 km s−1 kpc−1. Our simulation of the influence of a spiral density wave has shown that the peculiar velocity of the Sun with respect to
the local standard of rest and the component (V
⊙)LSR depend significantly on the Sun’s phase in the spiral wave. 相似文献
12.
David G. Russell 《Journal of Astrophysics and Astronomy》2009,30(2):93-118
The value of Hubble parameter (H0) is determined using the morphologically type dependent Ks-band Tully-Fisher Relation (K-TFR). The slope and zero point are
determined using 36 calibrator galaxies with ScI morphology. Calibration distances are adopted from direct Cepheid distances,
and group or companion distances derived with the Surface Brightness Fluctuation Method or Type Ia Supernova. It is found
that a small morphological type effect is present in the K-TFR such that ScI galaxies are more luminous at a given rotational
velocity than Sa/Sb galaxies and Sbc/Sc galaxies of later luminosity classes. Distances are determined to 16 galaxy clusters
and 218 ScI galaxies with minimum distances of 40.0 Mpc. From the 16 galaxy clusters a weighted mean Hubble parameter of H0 = 84.2 ± 6 km s−1 Mpc−1 is found. From the 218 ScI galaxies a Hubble parameter of H0 = 83.4 ± 8 km s−1 Mpc−1 is found. When the zero point of K-TFR is corrected to account for recent results that find a Large Magellanic Cloud distance
modulus of 18.39±0.05, a Hubble parameter of 88.0 ± 6 km s−1 Mpc−1 is found. Effects from Malmquist bias are shown to be negligible in this sample as galaxies are restricted to a minimum rotational
velocity of 150 km s−1. It is also shown that the results of this study are negligibly affected by the adopted slope for the K-TFR, inclination
binning, and distance binning. A comparison with the results of the Hubble Key Project (Freedman et al. 2001) is made. Discrepancies between the K-TFR distances and the HKP I-TFR distances are discussed. Implications for Λ-CDM
cosmology are considered with H0 = 84 km s−1 Mpc−1. It is concluded that it is very difficult to reconcile the value of H0 found in this study with ages of the oldest globular
clusters and matter density of the universe derived from galaxy clusters in the context of Λ-CDM cosmology. 相似文献
13.
The local expansion field (v
220 <1200 km s-1) and the cosmic expansion field out to 30 000 km s-1 are characterized by H
0 = 58 [km s-1 Mpc-1]. While the random error of this determination is small (± 2 units), it may still be affected by systematic errors as large
as ±10%>. The local expansion is outlined by Cepheids and by Cepheid-calibrated TF distances of a complete sample of field
galaxies and by nearby groups and clusters; the cosmic expansion is defined by Cepheid-calibrated SNe Ia. The main source
of systematic errors are therefore the shape and the zero point of the P-L relation of Cepheids and its possible dependence
on metallicity. GAIA will essentially eliminate these systematic error sources. Another source of systematic error is due
to the homogenization of SNe Ia as to decline rate Δm
15 and color (B-V). GAIA will discover most of the 1100 SNe Ia within 10 000 km s-1, which will occur during its four-year lifetime. If their photometric parameters can be determined from the ground, they
will fix the dependence of the SNe Ia luminosity on Δ m
15 and (B-V) with high accuracy. At the same time they will yield exquisite distances to an equal number of field galaxies. – GAIA will
also revolutionize the very local distance scale by determining fundamental distances of the companion galaxies of the Milky
Way and even of some spirals in- and possibly outside the Local Group from their rotation curves seen in radial velocities
and proper motions. Moreover, GAIA will obtain trigonometric parallaxes of RR Lyrae stars, of red giants defining the TRGB,
of stars on the ZAMS, of White Dwarf defining their cooling sequence, and of globular clusters, and determine the metallicity
dependence of these distance indicators. It will thus establish a self-controlling network of distance indicators within the
Local Group and beyond.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
A. I. Yatsenko 《Astrophysics and Space Science》1988,142(1-2):85-88
Summary In this paper the results of the research of the stars proper motions Trapezium components are reported. They are: the galactic
coordinates of the solar aprx and the Sun velocity (L
⊙=43±18°,B
⊙=+28±13°,V
⊙=13±4 km s−1), the dispersion of peculiar velocities in the direction of the galactic coordinates for the above mentioned stars (σ
l
=±11 km s−1, σ
b
=±7 km s−1).The attained accuracy of the proper motions (±0.005″ yr−1) is shown to be insufficient to the study of internal space motions in these systems. At present the work to increase the
relative proper motions accuracy for multiple system components and to improve reductions from the relative to absolute proper
motions, is being carried out in the Main Astronomical Observatory (Academy of Sciences of the Ukrainian SSR). The new catalogue
of the AGK3 stars is composed now in the vicinity of the galactic equator in order to improve reductions from the relative
to absolute proper motions. The r.m.s. errors of the proper motions, obtained in the AGK3 system, are ±0.005″ yr−1. 相似文献
15.
Coronal spectra during the total solar eclipse of 1980 February 16, were obtained in the 6374Å [Fex] line using a multislit spectrograph. These spectra have a dispersion of 2.5 Å mm-1. The observed line profiles from 1.1 to 1.7 R⊙ with a spatial resolution of 10 × 22 arcsec2, give half-widths that vary between 0.6 Å and 2.4Å. A large number of locations have half-widths around 1.3 Å corresponding to a temperature of 4.6 × 106 K. If temperature of the order of 1.3 × 106 K are typical of the regions that emit [Fex], then turbulent velocities of ~ 30 km s-1 need to be invoked for the enhanced line broadening. The line-of-sight velocities measured range between +14 km s-1 to -17 km s-1. Most of the locations have velocities less than ±5 km s-1. From these observations we conclude that corona does not show any localized differential mass motion and that it co-rotates with the photospheric layers deeper down. 相似文献
16.
V. V. Bobylev 《Astronomy Letters》2010,36(9):634-644
We analyze the three-dimensional kinematics of about 82 000 Tycho-2 stars belonging to the red giant clump (RGC). First, based
on all of the currently available data, we have determined new, most probable components of the residual rotation vector of
the optical realization of the ICRS/HIPPARCOS system relative to an inertial frame of reference, (ω
x
, ω
y
, ω
z
) = (−0.11, 0.24, −0.52) ± (0.14, 0.10, 0.16) mas yr−1. The stellar proper motions in the form μα cos δ have then be corrected by applying the correction ω
z
= −0.52 mas yr−1. We show that, apart from their involvement in the general Galactic rotation described by the Oort constants A = 15.82 ± 0.21 km s−1 kpc−1 and B = −10.87 ± 0.15 km s−1 kpc−1, the RGC stars have kinematic peculiarities in the Galactic yz plane related to the kinematics of the warped stellar-gaseous Galactic disk. We show that the parameters of the linear Ogorodnikov-Milne
model that describe the kinematics of RGC stars in the zx plane do not differ significantly from zero. The situation in the yz plane is different. For example, the component of the solid-body rotation vector of the local solar neighborhood around the
Galactic x axis is M
32− = −2.6 ± 0.2 km s−1 kpc−1. Two parameters of the deformation tensor in this plane, namely M
23+ = 1.0 ± 0.2 km s−1 kpc−1 and M
33 − M
22 = −1.3 ± 0.4 km s−1 kpc−1, also differ significantly from zero. On the whole, the kinematics of the warped stellar-gaseous Galactic disk in the local
solar neighborhood can be described as a rotation around the Galactic x axis (close to the line of nodes of this structure) with an angular velocity −3.1 ± 0.5 km s−1 kpc−1 ≤ ΩW ≤ −4.4 ± 0.5 km s−1 kpc−1. 相似文献
17.
E. V. Glushkova M. V. Zabolotskikh S. E. Koposov O. I. Spiridonova V. V. Vlasyuk A. S. Rastorguev 《Astronomy Letters》2010,36(1):14-26
We present the results of our BV R
c
I
c
CCD photometry for six Galactic open star clusters toward the Perseus spiral armperformed at the Special Astrophysical Observatory
of the Russian Academy of Sciences. Based on these data and using JHK
s
photometry from the 2MASS catalog, we have determined the ages, distances, and color excesses for the clusters: 710 Myr,
2960−340+400 pc, 0·
m
56 ± 0·
m
04 (King 13); 130 Myr, 3010−280+300 pc, 0·
m
69 ± 0·
m
04 (King 18); 560 Myr, 2630−270+310 pc, 0·
m
69 ± 0·
m
08 (King 19); 160 Myr, 1750−70+80 pc, 0·
m
77 ± 0·
m
05 (King 20); 250 Myr, 5220−320+350 pc, 0·
m
70 ± 0·
m
09 (NGC 136); 320 Myr, 3390−200+210 pc, 0·
m
43 ± 0·
m
03 (NGC 7245). 相似文献
18.
19.
B. Khalesseh 《Astrophysics and Space Science》1998,260(3):299-307
New radial velocity measurements of the Algol-type eclipsing binary AI Dra, based on Reticon observations, are presented.
The velocity measures themselves are based on fitting theoretical profiles, generated by a physical model of the binary, to
the observed cross-correlation function (ccf). Such profiles match this function very well, much better in fact that Gaussian
profiles which are generally used. Measuring the ccf's with Gaussian profiles yields following results: mp sin3 i=2.55± 0.05m⊙, ms sin3 i = 1.14 ± 0.03m⊙, (ap + as) sin i=7.34 ±0.05R⊙, and mp/ms =2.23± 0.05. Where as measuring the ccf's with theoretical profiles yields a mass ratio of 2.33 and following results:
mp sin3 i=2.84± 0.05m⊙, ms sin3 i=1.22 ± 0.03m⊙, (ap +as) sin i=7.56± 0.05R⊙.
The system comprising a semi-detached configuration. From the solution of a previously published light curved and combining
it's results with the spectroscopic orbit, one can lead to the following physical parameters: mp =2.99m⊙, ms =1.28m⊙, > Tp < =9600 K, > Ts < =5400 K, > Rp < =2.35R⊙, > Rs < =2.12R⊙. The system comprising an AO primary and a secondary of G2 spectral type.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献