共查询到20条相似文献,搜索用时 62 毫秒
1.
Chandrasekhar T. Ashok N. M. Tej Anandamayee Mondal Soumen Watson P. V. 《Earth, Moon, and Planets》1998,81(2):111-121
During the recent apparition of comet Hale—Bopp (1995 O1) near infrared photometric observations were carried out in the J,
H, K filter bands and also in the 3.0—3.4 μm region at the 1.2 m telescope at Gurushikkar, India. The effective temperature
of the comet was substantially higher than the equilibrium blackbody temperature. A mean superheat value of 1.83 was derived
in the post-perihelion phase which implies that a large fraction of the grain population are made up of small and hot grains
with radii <0.5 μm. High albedo values of ∼0.4 were also derived in the scattering angle range 135° to 160° which could explain
the unusual brightness of comet Hale—Bopp.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
The Franck-Condon factors andr-centroids, which are very closely related to vibrational transition probabilities, have been evaluated by the more reliable
numerical integration procedure for the bands of A
2 Δ - X2 πr system of astrophysical molecule GeH, using a suitable potential. The dissociation energy for the electronic ground state
of astrophysical molecule GeH has been estimated precisely as D
0
0 = 2.69 ± 0.05 eV by fitting the empirical potential function to the experimental potential energy curve using correlation
coefficient.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Hitoshi Hasegawa Takashi Ichikawa Shinsuke Abe Shiomo Hamamura Koji Ohnishi Jun-Ich Watanabe 《Earth, Moon, and Planets》1997,78(1-3):353-358
Near-infrared photometric and polarimetric observations of comet Hale-Bopp (1995 O1) using KONIC (Kiso Observatory Near-Infrared
Camera) are reported. Observations were carried out on March 18 UT and April 26 UT 1997, when the heliocentric distances of
the comet were 0.94 and 1.02 AU, and the phase angles were 48.5 deg and 32.9 deg, respectively. In the J, H, and K′ bands,
we obtained linear polarization of the near-nucleus region of 16.4 ± 1.2, 18.8 ± 1.3, and 15.1 ± 0.9 percent on March 18UT
and 7.1 ± 1.1, 8.9 ± 1.0, and 6.9 ± 0.6 percent on April 26, respectively. These values were higher than those observed for
1P/Halley. The maximum polarization was found at H band on both dates. Polarization maps showed higher polarization regions
toward the anti-solar direction in the J and H bands. No distinct correlation was found between high polarization regions
and bright regions. The projected expansion velocity of the arc structure of the dust jet was 375 ± 35.7 m/s on 17–19 March.
The periodicity was found to be 11.1 ± 2.8 hours.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
The multicolor light curves (UBVRI) of HU Vir have been analyzed to study starspots for epochs 1987 and 1989. The term 'photometric
imaging' has been used for predicting cool surface spots by photometric data. Assuming the number of spots and the area are
about the same for the two hemispheres, the distributive solar analogy is introduced as a tool to constrain free values of
spot parameters into unique values. Therefore, final fitting parameters are claimed unique in a sense that they are independent
of free initial guesses. The light and color variations of HU Vir are better explained without polar spots. Finally, the spots
are found to be ∼ 1600 K cooler than the T∼ 5000 K of this cool subgiant and cover ∼ %13.9 of the total surface at ±8.0 degrees
from the equator for the epoch 1987. The spots at the epoch 1989 are found to be ∼ 2040 K cooler covering ∼ % 12.7 area at
± 27°.7 latitudes. Problems of photometric imaging and possible solutions with distributive solar analogy have been discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
Near infrared measurements in the J, H and K bands have been carried out for a number of symbiotic stars with the 1.5 m telescope
at the Rothney Astrophysical Observatory (RAO). A comparison with the earlier observations shows that the S-type symbiotic
stars do not have any significant variation in the infrared flux over the past five years. However a small variation ∼ 0.3
magnitude in the infrared flux has been detected for CH Cygni. The observations of HM Sagittae show large decreases in the
infrared flux compared to the previous measurements. The variability in the infrared fluxes of both these objects could be
attributed to a variation in the temperature due to the cooling of the dust shell. The variability observed for V1016 Cygni
is found consistent with the previous measurements. 相似文献
6.
V. P. Arkhipova V. G. Klochkova E. L. Chentsov V. F. Esipov N. P. Ikonnikova G. V. Komissarova 《Astronomy Letters》2006,32(10):661-670
We present the results of spectroscopic and photometric observations for the B star StHα62 with an IR excess, a post-AGB candidate identified with the IR source IRAS 07171+1823. High-resolution spectroscopy has allowed the λ4330–7340 Å spectrum of the star to be identified: it contains absorption lines of an early B star and emission lines of a gaseous shell. The residual line intensities have been measured. The heliocentric radial velocities measured from absorption lines of the star and emission lines of the shell are 〈V r 〉 = +45 ± 1 and +52 ± 1 km s?1, respectively. The line-of-sight velocities of gas-dust clouds determined from the interstellar Na I lines are 12 and 33 km s?1. The He I λ5876 Å line exhibits a P Cyg profile, which is indicative of an ongoing mass loss by the star. The expansion velocity of the outer shell estimated from forbidden lines is 12–13 km s?1. Quantitative classification gives the spectral type B0.51 for the star. The parameters of the gaseous shell have been determined: N e = 3.1 × 103 cm?3 and T e ~ 21 000 K. Over 4 years of its observations, the star showed rapid irregular light variations with the amplitudes ΔV = We present the results of spectroscopic and photometric observations for the B star StHα62 with an IR excess, a post-AGB candidate
identified with the IR source IRAS 07171+1823. High-resolution spectroscopy has allowed the λ4330–7340 ? spectrum of the star
to be identified: it contains absorption lines of an early B star and emission lines of a gaseous shell. The residual line
intensities have been measured. The heliocentric radial velocities measured from absorption lines of the star and emission
lines of the shell are 〈V
r
〉 = +45 ± 1 and +52 ± 1 km s−1, respectively. The line-of-sight velocities of gas-dust clouds determined from the interstellar Na I lines are 12 and 33
km s−1. The He I λ5876 ? line exhibits a P Cyg profile, which is indicative of an ongoing mass loss by the star. The expansion velocity
of the outer shell estimated from forbidden lines is 12–13 km s−1. Quantitative classification gives the spectral type B0.51 for the star. The parameters of the gaseous shell have been determined:
N
e
= 3.1 × 103 cm−3 and T
e
∼ 21 000 K. Over 4 years of its observations, the star showed rapid irregular light variations with the amplitudes ΔV =
, ΔB =
, and ΔU =
and no color-magnitude correlation. We estimate the total extinction for the star from our photometric observations as A
v
=
. Near-IR observations have revealed dust radiation with a temperature of ∼1300 K. We estimate the distance to StHα62 to be
r = 5.2 ± 1.2 kpc by assuming that the star is a low-mass (M = 0.55 ± 0.05 M
⊙) protoplanetary nebula.
Original Russian Text ? V.P. Arkhipova, V.G. Klochkova, E.L. Chentsov, V.F. Esipov, N.P. Ikonnikova, G.V. Komissarova, 2006,
published in Pis’ma v Astronomicheskiĭ Zhurnal, 2006, Vol. 32, No. 10, pp. 737–747. 相似文献
7.
S. K. Ghosh B. Mookerjea T. N. Rengarajan S. N. Tandon R. P. Verma 《Journal of Astrophysics and Astronomy》2001,22(2-3):173-185
Three Galactic star forming regions associated with W3(OH), S209 and S187 have been simultaneously mapped in two trans-IRAS
far infrared (FIR) bands centered at ≈140 and 200μm using the TIFR 100 cm balloon borne FIR telescope. These maps show extended
FIR emission with structures. The HIRES processed IRAS maps of these regions at 12, 25, 60 & 100 ìm have also been presented
for comparison. Point-like sources have been extracted from the longest waveband TIFR maps and searched for associations in
the other five bands. The diffuse emission from these regions have been quantified, which turns out to be a significant fraction
of the total emission. The spatial distribution of cold dust (T < 30 K) for two of these sources (W3(OH) & S209), has been
determined reliably from the maps in TIFR bands. The dust temperature and optical depth maps show complex morphology. In general
the dust around S209 has been found to be warmer than that in W3(OH) region. 相似文献
8.
Franck-Condon Factors and r-Centroids of Certain Band Systems of Astro Physical Molecules SO and TiO
The Franck-Condon (FC) factors (transition probabilities) and r-centroids have been evaluated by the reliable numerical integration
procedure for the bands of the b1 Σ+ −x3 Σ− system of astrophysical molecule SO. Also for the bands of f1Δ − a1 Δ and e1 Σ+
− d1 Σ+ systems of astrophysical molecule TiO, the FC factors and r-centroids have been evaluated, using a suitable potential.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
R.R. Reddy Y. Nazeer Ahammed B. Sasikala Devi K. Rama Gopal P. Abdul Azeem T.V.R. Rao 《Astrophysics and Space Science》2002,281(4):729-741
The true experimental potential energy curves for the electronic ground states of astrophysically important TaO, TaS, ZrS
and SiO+molecules are constructed by using the Rydberg–Klein–Rees method as modified by Vanderslice et al. The ground state dissociation
energies are determined by curve fitting techniques using the five parameters Hulburt-Hirschfelder (H-H) function. The estimated
dissociation energies are 8.19 ± 0.17, 6.9 ±0.14, 5.89 ± 0.12 and 5.75 ± 0.12 eVfor TaO, TaS, ZrS and SiO+ respectively. These values are in good agreement with the literature values. The r-centriods and Franck–Condon factors (FC
Factors) for the bands of K
2
φ
5/2
- X
2
Δ
3/2
(K-X) system of TaO, A-X
2 Δ (A-X) and B-X
2 Δ (B-X)systems of TaS, B
1 Π - X1 Σ+
(B-X) system of ZrS and B
2Σ+ - X2 Σ+
(B-X) and A
2 Π - X2 Σ+
(A-X)systems of SiO+ molecules have been calculated. The Franck–Condon factors (FC factors) are evaluated by the approximate analytical methods
of Jarmain and Fraser. The absence of the bands of these systems is explained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
John K. Webb Michael T. Murphy Victor V. Flambaum Stephen J. Curran 《Astrophysics and Space Science》2003,283(4):565-575
We report results from a third sample of quasar absorption line spectra from the Keck telescope which has been studied to
search for any possible variation of the fine structure constant, α. This third sample, which is larger than the sum of the
two previously published samples, shows the same effect, and also gives, as do the previous two samples, a significant result.
The combined sample yields a highly significant effect, Δα = (αz - α0 )/α0 = -0.57 ± 0.10 × 10-5, averaged over the redshift range 0.2 < z < 3.7. We include a brief discussion of small-scale kinematic structure in quasar
absorbing clouds. However, kinematics are unlikely to impact significantly on the averagednon-zeroΔα /α above, and we have
so far been unable to identify any systematic effect which can explain it. New measurements of quasar spectra obtained using
independent instrumentation and telescopes are required to properly check the Keck results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
A series of daytime observations of the Sun and major planets are obtained at the mountain astronomical station of the Pulkovo
Observatory using the Ertel-Struve meridian instruments. A series of declinations of Solar System bodies and major planets
includes 4057 positions and that of right ascensions of Solar System bodies comprising 2057 positions. Based on the joint
processing of observations of the Sun, Mercury, Venus, and Mars obtained with the Ertel-Struve vertical circle and large transit
instrument, the orientation elements of the DE200/LE200 dynamic coordinate system, namely, a correction for the right ascensions
of FK5 stars ΔA = +0.127″ ± 0.033″, a correction for declinations of FK5 stars ΔD = +0.056″ ± 0.011″, a correction for the ecliptic inclination Δɛ = −0.044″ ± 0.012″, and a correction for the average longitude
of the Sun ΔL = −0.083″±0.035″, are determined with respect to the stellar coordinate system. 相似文献
12.
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
13.
A. Ivanchik P. Petitjean E. Rodriguez D. Varshalovich 《Astrophysics and Space Science》2003,283(4):583-588
The possible cosmological variation of the proton-to-electron mass ratio μ = m
p
/m
e was estimated by measuring the H2 wavelengths in the high-resolution spectrum of the quasar Q 0347-382. Our analysis yielded an estimate for the possible deviation
ofμ value in the past, 10 Gyr ago: for the unweighted valueΔ μ / μ = (3.0±2.4)×10-5; for the weightedvalueΔ μ / μ = (5.02±1.82)×10-5.Since the significance of the both results does not exceed3σ, further observations are needed to increase the statistical
significance. In any case, this result may be considered as the most stringent estimate on an upper limit of a possible variation
of μ (95% C.L.):|Δ μ / μ| < 8× 10-5 .This value serves as an effective tool for selection of models determining a relation between possible cosmological deviations
of the fine-structure constant α and the elementary particle masses (mp, me, etc.).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
The Tully-Fisher (TF) or the luminosity-linewidth relations of the galaxies in the Eridanus group are constructed using the
HI rotation curves and the luminosities in the optical and in the near-infrared bands. The slopes of the TF relations (absolute
magnitudevs log2V
flat) are −8.6 ± 1.1, −10.0 ±1.5, −10.7 ±2.1, and −9.7 ±1.3 in the R, J, H, and K bands respectively for galaxies having flat
HI rotation curves. These values of the slopes are consistent with those obtained from studies of other groups and clusters.
The scatter in the TF relations is in the range 0.5-1.1 mag in different bands. This scatter is considerably larger compared
to those observed in other groups and clusters. It is suggested that the larger scatter in the TF relations for the Eridanus
group is related to the loose structure of the group. If the TF relations are constructed using the baryonic mass (stellar
+HI + Helium mass) instead of the stellar luminosity, nearly identical slopes are obtained in the R and in the near-infrared
bands. The baryonic TF (baryonic massvs log2V
flat) slope is in the range 3.5–4.1. 相似文献
15.
A. V. Meshcheryakov M. G. Revnivtsev M. N. Pavlinsky I. Khamitov I. F. Bikmaev 《Astronomy Letters》2010,36(10):738-751
The variability of the optical and X-ray fluxes from the binary GS 1826-238 is investigated. An epoch-folding analysis of
the optical data obtained with the RTT-150 telescope in 2003–2004 has revealed periodic brightness variations in the source
with a period P
orb = 2.24940 ± 0.00015 h with a high statistical significance. When estimating the detection significance of the periodic signal,
we have specially taken into account the presence of a powerful aperiodic component (“red noise”) in the source’s brightness
variability. The source’s power density spectra in the frequency range ∼10−5–0.01 Hz have been obtained. We have detected a statistically significant break in the power density spectrum of GS 1826-238
at a frequency ν
br ≈ (8.48 ± 0.14) × 10−5 Hz in both optical and X-ray energy bands. We have estimated the orbital period of the binary GS 1826-238 using the correlation
between the break frequency in the power density spectrum and the orbital period of binaries, P
orb ∝ 1/ν
br, found by Gilfanov and Arefiev (2005): P
orb = 3.7 ± 0.8 h and P
orb = 11.3 ± 5.9 h when using Sco X-1 and 1H 16267-273, respectively, as reference sources. It seems to us that the method for
estimating the orbital periods of low-mass X-ray binaries using the correlation P
orb ∝ 1/ν
br may turn out to be very promising, especially for persistent low-luminosity X-ray binaries. 相似文献
16.
W. P. S. Meikle 《Monthly notices of the Royal Astronomical Society》2000,314(4):782-792
The absolute luminosities and homogeneity of early-time infrared (IR) light curves of type Ia supernovae are examined. Eight supernovae are considered. These are selected to have accurately known epochs of maximum blue light as well as having reliable distance estimates and/or good light curve coverage. Two approaches to extinction correction are considered. Owing to the low extinction in the IR, the differences in the corrections via the two methods are small. Absolute magnitude light curves in the J , H and K bands are derived. Six of the events, including five established 'branch-normal' supernovae, show similar coeval magnitudes. Two of these, supernovae (SNe) 1989B and 1998bu, were observed near maximum infrared light. This occurs about 5 d before maximum blue light. Absolute peak magnitudes of about −19.0, −18.7 and −18.8 in J , H and K respectively were obtained. The two spectroscopically peculiar supernovae in the sample, SNe 1986G and 1991T, also show atypical IR behaviour. The light curves of the six similar supernovae can be represented fairly consistently with a single light curve in each of the three bands. In all three IR bands the dispersion in absolute magnitude is about 0.15 mag, and this can be accounted for within the uncertainties of the individual light curves. No significant variation of absolute IR magnitude with B -band light curve decline rate, Δ m 15 ( B ), is seen over the range 0.87<Δ m 15 ( B )<1.31. However, the data are insufficient to allow us to decide whether or not the decline rate relation is weaker in the IR than in the optical region. IR light curves of type Ia supernovae should eventually provide cosmological distance estimates that are of equal, or even superior, quality to those obtained in optical studies. 相似文献
17.
We have previously presented 5.7 σ evidence for a smaller αat redshifts 0.2 < zabs < 3.7 from a sample of 128 Keck/HIRES quasar absorption systems: Δα/α = (-0.57 ± 0.10) x10-5. A non-zero <Δα/α manifests itself as a distinct pattern of shifts in the measured absorption line wavelengths. The statistical
error is now small: we do detect small line shifts in the HIRES data. Whether these shifts are due to systematic errors or
due to real variation in α is now the central question. Here we summarize the two potentially most important systematic effects:
atmospheric dispersion and isotopic abundance evolution. Previously, these have been difficult to quantify/model but here
we find that neither of them can explain our results. Furthermore, the HIRES spectra themselves contain no evidence for these
effects. Independent measurements of Δα/α with a different telescope and spectrograph are now crucial if we are to rule out
or confirm the present evidence for a variable α.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Johannes Reetz 《Astrophysics and Space Science》1999,265(1-4):171-174
The absolute solar oxygen abundance,ε ⊙ = 8.80± 0.06, has been determined from various oxygen abundance indicators in different solar
atlases, and a new method is proposed to test collision rate coefficientsfor the NLTE model of OI.Using effective temperatures
derived from Balmer lines, oxygen abundances from O triplets in 83 solar-type stars within the solar neighborhood spanning
a metallicity range of [Fe/H] = −2.3 ... +0.4 have been determined.NLTE effects are not negligible, especially in warm stars(Teff ≥ 5800) with [Fe/H] ≥ −0.5.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
J. C. Pandey K. P. Singh S. A. Drake R. Sagar 《Journal of Astrophysics and Astronomy》2005,26(4):359-376
BVR photometric and quasi-simultaneous optical spectroscopic observations of the star HD 81032 have been carried out during
the years 2000-2004. A photometric period of 18.802 ± 0.07d has been detected for this star. A large group of spots with a
migration period of 7.43 ± 0.07 years is inferred from the first three years of the data. Hα and CaII H and K emissions from
the star indicate high chromospheric activity. The available photometry in the BVRIJHK bands is consistent with the spectral
type of K0IV previously found for this star. We have also examined the spectral energy distribution of HD 81032 for the presence
of an infrared colour excess using the 2MASS JHK and IRAS photometry, but found no significant excess in any band above the
normal values expected for a star with this spectral type. We have also analyzed the X-ray emission properties of this star
using data obtained by the ROSAT X-ray observatory during its All-Sky Survey phase. An X-ray flare of about 12 hours duration
was detected during the two days of X-ray coverage obtained for this star. Its X-ray spectrum, while only containing 345 counts,
is inconsistent with a single-temperature component solar-abundance coronal plasma model, but implies either the presence
of two or more plasma components, nonsolar abundances, or a combination of both of these properties. All of the above properties
of HD 81032 suggest that it is a newly identified, evolved RS CVn binary. 相似文献
20.
We investigate the regime of chromospheric oscillations at the bases of coronal holes and compare them with the oscillations
in the quiet chromosphere outside coronal holes using time series of spectrograms taken at different times in eight quiet
regions on the Sun. As the oscillation parameter being studied, we have chosen the central intensity of the chromospheric
Ca II K and H and 849.8-nm lines. The intensity measurements at all spatial points (along the spectrograph slit) have been
subjected to a standard Fourier analysis. For the identified areas of the networks, cells, and network boundaries, we have
calculated the integrated oscillation powers in several frequency bands. For all frequency bands, the powers of the intensity
oscillations at the formation level of the Ca II resonance doublet line cores have been found to be enhanced at the bases
of coronal holes approximately by a factor of 1.5. For the “three-minute” band, this enhancement is more pronounced in the
network than in the cell, while the opposite is true for the “five-minute” band. The power in the five-minute band is higher
than that in the three-minute one both at the bases of coronal holes and outside them, but this ratio in the network for a
coronal hole is higher (1.40 ± 0.25 and 1.30 ± 0.10). We interpret this fact and the fact that the power of the three-minute
oscillations for nonmagnetic regions changes with height differently at the base of a coronal hole and outside it as an increase
in the importance of magnetoacoustic portals at the chromospheric base of the coronal hole. 相似文献