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1.
We report on our observing programme to obtain integrated spectrophotometry, intermediate- and high-resolution major-axis
spectra, and UBR surface photometry of a representative sample of ∼ 200galaxies in the nearby field. The main goal of this programme is to
provide a comparison sample for high-redshift studies and to study the variation in star formation rates (SFRs), star formation
history (SFH),excitation, metallicity, and internal kinematics over a wide range of galaxy luminosities and morphological
types. In particular, we extend the work of Kennicutt (1992) to lower-luminosity systems. We present the main results of our
analysis so far. In these proceedings, we condense the two atlases presented of 1) images and radial surface brightness profiles
and colour profiles, and 2) images and integrated spectra into several example images, profiles and spectra, showing the general
trends observed. For the original atlases we refer the reader to the electronic distribution on CDROM or as available on the
Web at http://www.astro.rug.nl/∼nfgs/.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
We present the first modern systematic study of local brightest cluster galaxy (BCG) profiles that extends to radii beyond
200h
-1kpc. Measuring the surface brightness profiles of BCGs out to large radii is critical for understanding the processes driving
their formation. The form of the profiles yields information about the current dynamical state, constrains the accretion history
of these galaxies, and places limits on any radially symmetric component of intracluster light. The observational challenges
associated with CCD photometry at low surface brightness levels have until now precluded such an analysis for a statistical
sample of BCGs. Utilizing drift-scan data and new techniques that we have developed, we extend upon previous work by modelling
the profiles for a sample of 31 clusters at z≃ that span a wide range in mass and dynamical state. We find that the BCGs in our sample generally are best fit using two-component
models consisting of inner and outer Sersic profiles. In this proceeding we present the preliminary results of our analysis
and discuss implications for current models of BCG formation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
The behaviour of pulsars at low radio-frequencies (below ≈ 50 MHz) remains poorly understood mainly due to very limited observational
data on pulsars at these frequencies. We report here our measurements of pulse profiles at 34.5 MHz of 8 pulsars using the
Gauribidanur Radio Telescope. None of the 8 pulsars show any significant interpulse emission at this frequency which conflicts
with an earlier claim from 25 MHz observations. With the exception of one pulsar (PSR 0943 + 10) all the observed pulsars
show turnovers at frequencies above 35 MHz in their spectra. We also report our attempts to study the short and long term
variations in the pulsar signals at this low frequency. 相似文献
4.
A high galactic latitude HI 21 cm-line absorption survey using the GMRT: I. Observations and spectra
Rekhesh Mohan K. S. Dwarakanath G. Srinivasan 《Journal of Astrophysics and Astronomy》2004,25(3-4):143-183
We have used the Giant Meterwave Radio Telescope (GMRT) to measure the Galactic HI 21-cm line absorption towards 102 extragalactic
radio continuum sources, located at high (|b| > 15°) Galactic latitudes. The Declination coverage of the present survey is δ}> - 45°. With a mean rms optical depth of ∼ 0.003, this is the most sensitive Galactic HI 21-cm line absorption survey to
date. To supplement the absorption data, we have extracted the HI 21-cm line emission profiles towards these 102 lines of
sight from the Leiden Dwingeloo Survey of Galactic neutral hydrogen. We have carried out a Gaussian fitting analysis to identify
the discrete absorption and emission components in these profiles. In this paper, we present the spectra and the components.
A subsequent paper will discuss the interpretation of these results. 相似文献
5.
We present some results from our submillimeter single-dish and aperture synthesis imaging surveys of protoplanetary disks
using the JCMT, CSO, and Submillimeter Array (SMA) on Mauna Kea, Hawaii. Employing a simple disk model, we simultaneously
fit the spectral energy distributions and spatially resolved submillimeter continuum emission from our SMA survey to constrain
disk structure properties, including surface density profiles and sizes. The typical disk structure we infer is consistent
with a fiducial accretion disk model with a viscosity parameter α≈0.01. Combined with a large, multiwavelength single-dish survey of similar disks, we show how these observations provide
evidence for significant grain growth and rapid evolution in the outer regions of disks, perhaps due to an internal photoevaporation
process. In addition, we discuss SMA observations of the disks in the Orion Trapezium (proplyds) in the context of disk evolution
in a more extreme environment. 相似文献
6.
Daniel Thomas Ralf Bender Ulrich Hopp Claudia Maraston Laura Greggio 《Astrophysics and Space Science》2003,284(2):599-602
We present kinematics and stellar population properties of 17 dwarf early-type galaxies in the luminosity range -14 ≥ M
B ≥ -19. Our sample fills the gap between the intensively studied giant elliptical and Local Group dwarf spheroidal galaxies.
The dwarf ellipticals of the present sample have constant velocity dispersion profiles within their effective radii and do
not show significant rotation, hence are clearly anisotropic. The dwarf lenticulars, instead, rotate faster and are, at least
partially, supported by rotation. From optical Lick absorption indices, we derive metallicities and element abundances. Combining
our sample with literature data of the Local Group dwarf spheroidals and giant ellipticals, we find a surprisingly tight linear
correlation between metallicity and luminosity over a wide range: -8 ≥ M
B ≥ -22. The α/Fe ratios of our dwarf ellipticals are significantly lower than the ones of giant elliptical galaxies, which
is in agreement with spectroscopy of individual stars in Local Group dwarf spheroidals. Our results suggest the existence
of a clear kinematic and stellar population dichotomy between dwarf and giant elliptical galaxies. This result is important
for theories of galaxy formation, because it implies that present-day dwarf ellipticals are not the fossiled building blocks
of giant ellipticals.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
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
8.
We present Lick line-index measurements for standard stars from Worthey’s list. The spectra were taken with the multislit
unit of the SCORPIO spectrograph at the 6-m Special Astrophysical observatory telescope. We describe in detail our method
of analysis and explain the importance of using the Lick index system for studying extragalactic globular clusters. Our results
show that the calibration of our instrumental system to the standard Lick system can be performed with high confidence.
The article was translated by the authors in English.
Published in Russian in Pis’ma v Astronomicheskiĭ Zhurnal, 2006, Vol. 32, No. 3, pp. 209–216. 相似文献
9.
Peter L. Gonthier Sarah A. Story Brian D. Clow Alice K. Harding 《Astrophysics and Space Science》2007,309(1-4):245-251
We present results of our pulsar population synthesis of normal and millisecond pulsars in the Galactic plane. Over the past
several years, a program has been developed to simulate pulsar birth, evolution and emission using Monte Carlo techniques.
We have added to the program the capability to simulate millisecond pulsars, which are old, recycled pulsars with extremely
short periods. We model the spatial distribution of the simulated pulsars by assuming that they start with a random kick velocity
and then evolve through the Galactic potential. We use a polar cap/slot gap model for γ-ray emission from both millisecond and normal pulsars. From our studies of radio pulsars that have clearly identifiable core
and cone components, in which we fit the polarization sweep as well as the pulse profiles in order to constrain the viewing
geometry, we develop a model describing the ratio of radio core-to-cone peak fluxes. In this model, short period pulsars are
more cone-dominated than in our previous studies. We present the preliminary results of our recent study and the implications
for observing these pulsars with GLAST and AGILE.
相似文献
10.
We present our results of high temporal resolution spectroscopic observation and study in Hα, Ca II, and He I lines for the 2B/M1.9 confined disk flare on September 9, 2001, combining with GOES soft X-ray (SXR) and Yohkoh hard X-ray (HXR) observations. Apparent redshifted and red-asymmetric profiles were observed in the initial phase. The redshift
lasted until the late phase. The derived velocity depends on both the spectral line and the used method. The redshift velocities
computed from the line centers of the observed emission profiles (υ0) are of the order of 10 km s−1 both inside and outside the streak area. However, the velocities determined from the excess profiles by the bisector method
(υ) are larger in the streak (18–50 km s−1). Both υ and the red full widths (RFWs) derived from the excess profiles show temporal variations similar to the HXR light-curve
in the streak area. Moreover, the Hα line wings of nonthermal characteristics, the redshift velocities, and the lifetime of
impulsive broadening suggest that the streak is related to nonthermal electron bombardment. Spectral simulations reveal that
we cannot reproduce the observed profiles in the three lines simultaneously with a set of parameters, indicating that the
flare atmosphere was not homogeneous along the line-of-sight. Most of the observed Hα profiles showed a ‘flat-top’ structure,
implying the flare plasma was optically thick for this line. The electron temperatures (Te) deduced from the line-center intensity of the three lines are similar and estimated to be higher than 7200 K. The obvious
central reversal of the Hα profiles due to absorption of materials in the impulsive phase lasted more than 2 min. However,
the far blue wings of the Ca II profiles in the impulsive phase showed low-intensity emission, which is suggestive of the
existence of large turbulence or macroscopic motion (> 50 km s−1), which is inconsistent with the current flare model. 相似文献
11.
J.J. Lockley J.H. Wood D.H.P. Jones S. Mineshige 《Astrophysics and Space Science》1999,266(4):453-465
A spectroscopic study of the frequently outbursting dwarf nova UY Pup has been undertaken whilst the system was in outburst.
The Hα andHβ line profiles in UY Pup are typical of low inclination dwarf novae after outburst maximum. No evidence for two
components is seen in the emission lines. Using radial velocity measurements of Hα, we find the best fit orbital period for
the system to be 10.22 ± 0.19 h(although we cannot with certainty rule out a period of 7.13 ± 0.14 h).We place limits on the
system parameters. We also present multicolour photometry of UY Pup in quiescence.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
We present the results of our studies of the cosmic-ray fluctuations in the frequency range 10−4−1.67 × 10−3 Hz based on energetic particle flux measurements on spacecraft in the solar wind, in the magnetosphere, and at Earth in the
11-year solar cycle. The cosmic-ray fluctuation spectrum is shown to have an 11-year modulation related to the solar cycle.
A different behavior of the level of energetic particle fluctuations measured in different regions of space is observed for
cosmic rays of different origins. We conclude that the new, previously unknown phenomenon of 11-year modulation of the cosmic-ray
fluctuation spectrum has been established. A possible explanation of this phenomenon is given. 相似文献
13.
A. Fritz B.L. Ziegler R.G. Bower I. Smail R.L. Davies 《Astrophysics and Space Science》2003,285(1):61-66
We explore the evolution of the early-type galaxy population in the rich cluster Abell 2390 at z=0.23. For this purpose, we have obtained spectroscopic data of 51 elliptical and lenticular galaxies with MOSCA at the 3.5
m telescope on Calar Alto Observatory. As our investigation spans both a broad range in luminosity (–22.3≤MB≤–:19.3)and a wide field of view (10′×10′), the environmental dependence of different formation scenarios can be analysed
in detail as a function of radius from the cluster center. In this paper, we present first results on the Faber-Jackson relation
and, for a subsample of 14 galaxies with morphological and structural parameters from HST, we also investigate the evolution
of the Kormendy relation and the Fundamental Plane. We find a mild luminosity evolution of the early-type galaxies in Abell
2390: our objects are on average brighter by m
B∼0.4 mag.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
L. K. Jian C. T. Russell J. G. Luhmann R. M. Skoug J. T. Steinberg 《Solar physics》2008,249(1):85-101
We present comprehensive surveys of 203 stream interaction regions (SIRs) and 124 interplanetary CMEs (ICMEs) during 1979 – 1988
using Pioneer Venus Orbiter (PVO) in situ solar-wind observations at 0.72 AU and examine the solar-cycle variations of the occurrence rate, shock association rate,
duration, width, maximum total perpendicular pressure (P
t), maximum dynamic pressure, maximum magnetic field intensity, and maximum velocity change of these two large-scale solar-wind
structures. The medians, averages, and histogram distributions of these parameters are also reported. Furthermore, we sort
ICMEs into three groups based on the temporal profiles of P
t, and we investigate the variations of the fractional occurrence rate of three groups of ICMEs with solar activity. We find
that the fractional occurrence rate of magnetic-cloud-like ICMEs declined with solar activity, consistent with our former
1-AU results. This study at 0.72 AU provides a point of comparison in the inner heliosphere for examining the radial evolution
of SIRs and ICMEs. The width of SIRs and ICMEs increases by 0.04 and 0.1 AU, respectively, and the maximum P
t decreases to about 1/3 from Venus to Earth orbit. In addition, our work establishes the statistical properties of the solar-wind
conditions at 0.72 AU that control the solar-wind interaction with Venus and its atmosphere loss by related processes.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
15.
We present the observations of the Irr galaxy IC 10 at the 6-m SAO telescope with the panoramic Multi-Pupil Fiber Spectrograph
(MPFS). Based on the results of these observations and our long-slit spectroscopy performed previously, we have investigated
the ionized-gas emission spectrum in the region of intense star formation and refined the gas metallicity estimates. We show
that the “diagnostic diagrams” constructed from our observations agree best with the new improved ionization models by Martin-Manjon
et al. Using these models, we have determined the electron density and gas ionization parameter and ionizing-cluster characteristics,
the age and mass, from the spectra of the investigated HII regions. The cluster ages and masses are shown to be within the
ranges 2.5–5 Myr and (0.2–1) × 105
M
⊗, respectively. 相似文献
16.
Thomas G. Moran Donald E. Jennings L. Drake Deming George H. McCabe Pedro V. Sada Robert J. Boyle 《Solar physics》2007,241(2):213-222
We present the first solar vector magnetogram constructed from measurements of infra-red Mg I 12.32-μm line spectra. Observations
were made at the McMath-Pierce Telescope using the Celeste spectrometer/polarimeter. Zeeman-split Stokes line spectra were
fitted with Seares profiles to obtain the magnetic field parameters. Maps of absolute field strength, line-of-sight angle,
and azimuth are presented. Analysis shows that the variation in field strength within a spatial resolution element, 2 arcseconds,
is greatest in the sunspot penumbra and that this is most likely caused by vertical field strength gradients, rather than
horizontal image smearing. Widths of the Zeeman-split σ components, assuming a formation layer thickness of 200 km, indicate that vertical field strength gradients can be as large
as 6.5 G/km in a penumbra. 相似文献
17.
We explore the detailed polarization behaviour of pulsar 0823 + 26 using the technique of constructing partial ‘mode-separated’
profiles corresponding to the primary and secondary polarization modes. The characteristics of the two polarization modes
in this pulsar are particularly interesting, both because they are anything but orthogonal and because the secondary mode
exhibits a structure seen neither in the primary mode nor in the total profile. The new leading and trailing features in the
secondary mode, which appear to represent a conal component pair, are interpreted geometrically on the basis of their width
and the associated polarization-angle traverse as an outer cone.
If the secondary-mode features are, indeed, an outer cone, then questions about the significance of the pulsar’s postcursor
component become more pressing. It seems that 0823 + 26 has a very nearly equatorial geometry, in that both magnetic poles
and the sightline all fall close to the rotational equator of the star. We thus associate the postcursor component with emission
along those bundles of field lines which are also equatorial and which continue to have a tangent in the direction of our
sight line for a significant portion of the star’s rotation cycle. It seems that in all pulsars with postcursor components,
this emission follows the core component, and all may thus have equatorial emission geometries. No pulsars with precursors
in this sense — including the Crab pulsar — are known.
The distribution of power between the primary and secondary modes is very similar at both 430 and 1400 MHz. Our analysis shows
that in this pulsar considerable depolarization must be occurring on time scales that are short compared to the time resolution
of our observations, which is here some 0.5–1.0 milliseconds. One of the most interesting features of the modeseparated partial
profiles is a phase offset between the primary and secondary modes. The secondary-mode ‘main pulse’ arrives some 1.5 ± 0.1‡
before the primary-mode one at 430 MHz and some 1.3 +0.1 ‡ at 21 cm. Given that the polar cap has an angular diameter of 3.36‡,
we consider whether this is a geometric effect or an effect of differential propagation of the two modes in the inner magnetosphere
of the pulsar. 相似文献
18.
Observations of the H272α recombination line towards the galactic centre show features near VLSR= 0, −50 and + 36 kms−1. We have combined the parameters of these features with the available H166α measurements to obtain the properties of the
ionized gas present along the line of sight and also in the ‘3 kpc arm’. For the line-of-sight ionized gas we get an electron
density around 7 cm−3 and a pathlength through it ∼ 10–60 pc. The emission measure and the electron temperature are in the range 500–2900 pc cm−6 and 2000–6000 K. respectively. The ionized gas in the 3 kpc arm has an electron density of 30 cm−3 and extends over 9 pc along the line of sight if we assume an electron temperature of 104 K. Using the available upper limit to the intensity of the H351α recombination line, we show that the distributed ionized
gas responsible for the dispersion of pulsar signals should have a temperature >4500 K. and a minimum filling factor of 20
per cent. We also show that recombination lines from the ‘warm ionized’ gas proposed by McKee & Ostriker (1977) should be
detectable in the frequency range 100–150 MHz towards the galactic centre with the sensitivity available at present. 相似文献
19.
A. P. Tsivilev 《Astronomy Letters》2009,35(10):670-678
We describe a method for determining the primordial helium abundance (Y
p) from radio recombination lines and present results of the first stage of our measurements. We analyze the observational
data for hydrogen and helium radio recombination lines from six Galactic H II regions obtained at different times. We have
found Y
p = 25.2−25.5% with an error of ±0.9% from four sources. 相似文献
20.
R. I. Kostyk 《Kinematics and Physics of Celestial Bodies》2011,27(4):175-182
Using a three-dimensional hydrodynamical model of the solar atmosphere, we calculated profiles of the Fe I λ 639.361 nm and
Fe II λ 523.462 nm lines with consideration for deviations from the local thermodynamic equilibrium. We determined heights
for intensity contrast reversal and for velocity sign reversal of convective elements. Both of these parameters depend strongly
on the convective velocity and intensity measured in the continuum. The larger the parameters, the greater is the atmosphere
altitude where the reversal takes place. We compared all the calculated relations with the observations obtained at the German
Vacuum Tower Telescope in Izana (Tenerife, Spain). In our opinion, the 3D hydrodynamical model of the solar atmosphere satisfactorily
describes all the main features of observed convective velocities and intensities. 相似文献