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1.
Observations on the 6-m telescope in the Hα line and in the continuum are reported for 10 dwarf companions of the galaxy M31:
And I, And II, And III, And V, And IX, And X, Cass dSph, Peg DSph, NGC147, NGC221, and one irregular dwarf galaxy in the background,
And IV. All the observed companions of M31 have current star formation rates (SFR) on the order of or less than 10−6 M⊙ /yr. On a “star formation rate-neutral hydrogen mass” diagram for galaxies in the local volume, the dwarf spheroidal companions
of Andromeda lie in the region of extremely low values for these parameters.
__________
Translated from Astrofizika, Vol. 49, No. 3, pp. 337–350 (August 2006). 相似文献
2.
The populations of B and Be-stars in the young open clusters NGC 7419 and NGC 659 are studied. Lowresolution spectral observations
in the region of the Hα line are used to study 34 members of NGC 7419 and additional spectra in the range λ3700-6200 ? are
obtained for 12 stars. During the period of our observations, four previously identified Be-stars manifested an absorption
profile for the Hα line. Emission in the Hα line is observed in the spectra of 21 objects. The members of the cluster NGC
7419 are classified as to spectral type. The position of the Be-stars on a two-color IR diagram and a comparison with the
position of the objects in other clusters with similar ages cast doubt on the existence of two starformation waves. Moderate
resolution spectra were obtained for 22 stars in the cluster NGC 659 over wavelengths of λ4050-5200 ? and for 7 objects in
the neighborhood of the Hα line. Emission is observed in both the Hα and Hβ lines for two of the five Be-stars that were studied,
while faint emission appears only in the Hα line in one of the stars. The other members of the cluster show no signs of emission
in these spectra. Teff, log g, and Vsini are estimated for the observed stars. It is found that 5 of the objects are not members of the cluster. 相似文献
3.
Isabel Márquez Josefa Masegosa Mariano Moles Jesús Varela Daniella Bettoni Giusseppe Galletta 《Astrophysics and Space Science》2003,284(2):711-714
We present the study of long slit spectra in the region ofHα emission line of a sample of 111 spiral galaxies with recognizable
and well defined spiral morphology and with a well determined environmental status, ranging from isolation to non-disruptive
interaction with satellites or companions. The form and properties of the rotation curves (RC) are considered as a function
of the isolation degree, morphological type, t, and luminosity. The line ratios are used to estimate the metallicity of all
the detected HII regions, thus producing a composite metallicity profile for different types of spirals. We have found that
isolated galaxies (ISO) tend to be of later types and lower luminosity than the interacting galaxies (INT). The outer parts
of the RC of ISO tend to be flatter than in INT, but they show similar relations between global parameters. The scatter of
the Tully-Fisher (TF) relation defined by ISO is significantly lower than that of INT. The [NII]/Hα ratios, used as a metallicity
indicator, show a clear trend between Z and t, with earlier spirals showing higher ratios; this trend is tighter when instead
of t the gradient of the inner RC, G, is used; no trend is found with the change in interaction status. The Z-gradient of
the disks depends on the type, being almost flat for early spirals, and increasing for later types. The [NII]/Hα ratios measured
for disk HII regions of INT are higher than for normal/ISO objects, even if all the galaxy families present similar distributions
of Hα Equivalent Width.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
R. P. Fender D. Rayner D. G. McCormick T. W. B. Muxlow G. G. Pooley R. J. Sault R. E. Spencer 《Monthly notices of the Royal Astronomical Society》2002,336(1):39-46
We describe H α , SCUBA and MERLIN imaging of the interacting galaxy pair NGC 4490 and 4485. We detect an H α filament emerging from the disc of NGC 4490 to a projected distance of 3 kpc which has counterparts in both the radio continuum and H i . The H i counterpart extends to a projected distance of ∼30 kpc from NGC 4490 and we argue that this is evidence that the giant H i envelope in this system has its origins in star formation. We use SCUBA and radio continuum data to attempt to place constraints on the distribution of dust with respect to the star forming regions. This analysis is limited by the lack of an independent estimate of the dust temperature, something that both 'SIRTF' and 'SOFIA' will be able to provide, however we find some evidence that most obscuring dust is not located within H ii regions themselves. 相似文献
5.
《New Astronomy》2015
Using the potential-density phase shift approach developed by the present authors in earlier publications, we estimate the magnitude of radial mass accretion/excretion rates across the disks of six nearby spiral galaxies (NGC 628, NGC 3351, NGC 3627, NGC 4321, NGC 4736, and NGC 5194) having a range of Hubble types. Our goal is to examine these rates in the context of bulge building and secular morphological evolution along the Hubble sequence. Stellar surface density maps of the sample galaxies are derived from SINGS 3.6 μm and SDSS i-band images using colors as an indicator of mass-to-light ratios. Corresponding molecular and atomic gas surface densities are derived from published CO (1-0) and HI interferometric observations of the BIMA SONG, THINGS, and VIVA surveys. The mass flow rate calculations utilize a volume-type torque integral to calculate the angular momentum exchange rate between the basic state disk matter and what we assume to be density wave modes in the observed galaxies. This volume-type integral contains the contributions from both the gravitational surface torque couple and the advective surface torque couple at the nonlinear, quasi-steady state of the wave modes, in sharp contrast to its behavior in the linear regime, where it contains only the contribution from the gravitational surface torque couple used by Lynden-Bell & Kalnajs in 1972. The potential-density phase shift approach yields angular momentum transport rates several times higher than those estimated using the Lynden-Bell and Kalnajs approach. And unlike Lynden-Bell and Kalnajs, whose approach predicts zero mass redistribution across the majority of the disk surface (apart from the isolated locations of wave-particle resonances) for quasi-steady waves, the current approach leads to predictions of significant mass redistribution induced by the quasi-steady density wave modes, enough for the morphological types of disks to evolve substantially within its lifetime. This difference with the earlier conclusions of Lynden-Bell and Kalnajs reflects the dominant role played by collisionless shocks in the secular evolution of galaxies containing extremely non-linear, quasi-steady density wave modes, thus enabling significant morphological transformation along the Hubble sequence during a Hubble time. We show for the first time also, using observational data, that stellar mass accretion/excretion is just as important, and oftentimes much more important, than the corresponding accretion/excretion processes in the gaseous component, with the latter being what had been emphasized in most of the previous secular evolution studies. 相似文献
6.
This is a study of the population of B and Be stars in the young, relatively poor, diffuse stellar clusters NGC 6871 and NGC
6913. High resolution spectra are used to study the Hα line of eleven stars in order to detect emission. Emission profiles
were found for three stars in the cluster NGC 6871; one of these is a known WR-star and the Be-star BD +35°3956 demonstrates
the transition from the B to the Be phase. Spectra of seven of the B stars revealed no traces of emission in the Hα line.
During the time of our observations, the Be star V1322 Cyg in the cluster NGC 6913 had a strong emission Hα line profile with
substantial variability in intensity and equivalent width. Moderate resolution spectra of seven stars in the cluster NGC 6871
over wavelengths of 4420-4960 ? and ten stars in the cluster NGC 6913 over wavelengths of 4050-5100 ? are used to classify
the series of B and Be stars spectrally and to estimate their T
eff
and log g. It was found that three of the stars are not members of the clusters NGC 6871 or NGC 6913.
Translated from Astrofizika, Vol. 52, No. 2, pp. 257–274 (May 2009). 相似文献
7.
Wahab Uddin Ramesh Chandra Syed Salman Ali 《Journal of Astrophysics and Astronomy》2006,27(2-3):267-276
We observed 4B/X17.2 flare in Hα from super-active region NOAA 10486 at ARIES, Nainital. This is one of the largest flares
of current solar cycle 23, which occurred near the Sun’s center and produced extremely energetic emission almost at all wavelengths
from γ-ray to radio-waves. The flare is associated with a bright/fast full-halo earth directed CME, strong type II, type III
and type IV radio bursts, an intense proton event and GLE. This flare is well observed by SOHO, RHESSI and TRACE. Our Hα observations
show the stretching/de-twisting and eruption of helically twisted S shaped (sigmoid) filament in the south-west direction
of the active region with bright shock front followed by rapid increase in intensity and area of the gigantic flare. The flare
shows almost similar evolution in Hα, EUV and UV. We measure the speed of Hα ribbon separation and the mean value is ∼ 70
km s-1. This is used together with photospheric magnetic field to infer a magnetic reconnection rate at three HXR sources at the
flare maximum. In this paper, we also discuss the energetics of active region filament, flare and associated CME. 相似文献
8.
F.P. Israel 《Astronomy and Astrophysics Review》1998,8(4):237-278
Summary. At a distance of 3.4 Mpc, NGC 5128 (Centaurus A) is by far the nearest active radio galaxy. It is often considered to be
the prototype Fanaroff-Riley Class I ‘low-luminosity’ radio galaxy, and as such it plays an important role in our understanding
of a major class of active galaxies. Its proximity has spawned numerous detailed investigations of its properties, yielding
unrivalled but still incomplete knowledge of its structure and dynamics.
The massive elliptical host galaxy is moderately triaxial and contains a thin, strongly warped disk rich in dust, atomic and
molecular gas and luminous young stars. Its globular cluster ensemble has a bimodal distribution of metallicities. Deep optical
images reveal faint major axis extensions as well as a system of filaments and shells. These and other characteristics are
generally regarded as strong evidence that NGC 5128 has experienced a major merging events at least once in its past.
The galaxy has a very compact, subparsec nucleus exhibiting noticeable intensity variations at radio and X-ray wavelengths,
probably powered by accretion events. The central object may be a black hole of moderate mass. Towards the nucleus, rich absorption
spectra of atomic hydrogen and various molecular species suggest the presence of significant amounts of material falling into
the nucleus, presumably ‘feeding the monster’. Emanating from the nucleus are linear radio/X-ray jets, becoming subrelativistic
at a few parsec from the nucleus. At about 5 kpc from the nucleus, the jets expand into plumes. Huge radio lobes extend beyond
the plumes out to to 250 kpc. A compact circumnuclear disk with a central cavity surrounds the nucleus. Its plane, although
at an angle to the minor axis of the galaxy, is perpendicular to the inner jets. The jet-collimating mechanism, probably connected
to the circumnuclear disk, appears to precess on timescales of order a few times 10 years.
This review summarizes the present state of knowledge of NGC 5128 and its associated radio source Centaurus A. Underlying
physical processes are outside its scope: they are briefly referred to, but not discussed.
Received 30 December 1997 相似文献
9.
S. Baes-Fischlmair W.W. Zeilinger J.-C. Vega-Beltran J.E. Beckman 《Astrophysics and Space Science》2003,284(2):735-738
It is assumed that the two-fold disc-wide symmetry of spirals is caused by density waves, but also the potential of a bar
component may have a significant influence on structural properties. The strength of the bar component appears to be anti-correlated
with the degree of symmetry of star-forming regions in the spiral arms (Rozas et al., 1998). We present new results of R and
Hα surface photometry of a sample of bright barred spirals. A photometric decompositon of the galaxy components is carried
out in order to make a more accurate measurement of the strength of the bar and its interrelation to gas and stars in the
disc.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Jonathan Braine P.-A. Duc U. Lisenfeld V. Charmandaris O. Vallejo S. Leon E. Brinks 《Astrophysics and Space Science》2002,281(1-2):407-408
We investigate the process of galaxy formation as can be observed in the only currently forming galaxies - the so-called Tidal
Dwarf Galaxies, hereafter TDGs - through observations of the molecular gas detected via its CO (Carbon Monoxide) emission.
These objects are formed of material torn off of the outer parts of a spiral disk due to tidal forces in a collision between
two massive galaxies. Molecular gas is a key element in the galaxy formation process, providing the link between a cloud of
gas and a bona fide galaxy. We have detected CO in 8 TDGs (Braine, Lisenfeld, Duc and Leon, 2000: Nature
403, 867; Braine, Duc, Lisenfeld, Charmandaris, Vallejo, Leon and Brinks: 2001, A&A
378, 51), with an overall detection rate of 80%, showing that molecular gas is abundant in TDGs, up to a few 108
M
⊙. The CO emission coincides both spatially and kinematically with the HI emission, indicating that the molecular gas forms
from the atomic hydrogen where the HI column density is high. A possible trend of more evolved TDGs having greater molecular
gas masses is observed, in accord with the transformation of HI into H2. Although TDGs share many of the properties of small irregulars, their CO luminosity is much greater (factor ∼ 100) than
that of standard dwarf galaxies of comparable luminosity. This is most likely a consequence of the higher metallicity (≳sim
1/3 solar) of TDGs which makes CO a good tracer of molecular gas. This allows us to study star formation in environments ordinarily
inaccessible due to the extreme difficulty of measuring the molecular gas mass. The star formation efficiency, measured by
the CO luminosity per Hα flux, is the same in TDGs and full-sized spirals. CO is likely the best tracer of the dynamics of
these objects because some fraction of the HI near the TDGs may be part of the tidal tail and not bound to the TDG. Although
uncertainties are large for individual objects, as the geometry is unknown, our sample is now of eight detected objects and
we find that the ‘dynamical’ masses of TDGs, estimated from the CO line widths, seem not to be greater than the ‘visible’
masses (HI + H2 + a stellar component). Although higher spatial resolution CO (and HI) observations would help reduce the uncertainties,
we find that TDGs require no dark matter, which would make them the only galaxy-sized systems where this is the case. Dark
matter in spirals should then be in a halo and not a rotating disk. Most dwarf galaxies are dark matter-rich, implying that
they are not of tidal origin. We provide strong evidence that TDGs are self-gravitating entities, implying that we are witnessing the
ensemble of processes in galaxy formation: concentration of large amounts of gas in a bound object, condensation of the gas,
which is atomic at this point, to form molecular gas and the subsequent star formation from the dense molecular component.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
11.
David K. Strickland 《Monthly notices of the Royal Astronomical Society》2007,376(2):523-533
We present the first imaging X-ray observation of the highly inclined ( i = 78°) Sab Seyfert 2 galaxy NGC 6810 using XMM–Newton , which reveals soft X-ray emission that extends out to a projected height of ∼7 kpc away from the plane of the galaxy. The soft X-ray emission beyond the optical disc of the galaxy is most plausibly extraplanar, although it could instead come from large galactic radius. This extended X-ray emission is spatially associated with diffuse Hα emission, in particular with a prominent 5-kpc-long Hα filament on the north-west of the disc. A fraction ≲35 per cent of the total soft X-ray emission of the galaxy arises from projected heights | z | ≥ 2 kpc . Within the optical disc of the galaxy the soft X-ray emission is associated with the star-forming regions visible in ground-based Hα and XMM–Newton optical monitor near-UV imaging. The temperature, supersolar α-element-to-iron abundance ratio, soft X-ray/Hα correlation, and X-ray to far-infrared (FIR) flux ratio of NGC 6810 are all consistent with local starbursts with winds, although the large base radius of the outflow would make NGC 6810 one of the few 'disc-wide' superwinds currently known. Hard X-ray emission from NGC 6810 is weak, and the total E = 2–10 keV luminosity and spectral shape are consistent with the expected level of X-ray binary emission from the old and young stellar populations. The X-ray observations provide no evidence of any active galactic nucleus activity. We find that the optical, IR and radio properties of NGC 6810 are all consistent with a starburst galaxy, and that the old classification of this galaxy as a Seyfert 2 galaxy is probably incorrect. 相似文献
12.
Regina E. Schulte-Ladbeck Igor O. Drozdovsky Michèle Belfort Ulrich Hopp 《Astrophysics and Space Science》2003,284(2):909-912
Formation paradigms for massive galaxies have long centered around two antipodal hypotheses – the monolithic-collapse and
the accretion/merger scenarios. Empirical data on the stellar contents of galaxy halos is crucial in order to develop galaxy
formation and assembly scenarios which have their root in observations, rather than in numerical simulations. The Hubble Space
Telescope (HST) has enabled us to study directly individual stars in the nearby E/S0 galaxies Cen A, NGC 3115, NGC 5102, and
NGC 404. We here present and discuss HST single-star photometry in V and I bands. Using color-magnitude diagrams and stellar
luminosity functions, we gauge the galaxies' stellar contents. This can be done at more than one position in the halo, but
data with deeper limiting magnitudes are desired to quantify the variation of metallicity with galactocentric radius. We here
compare the color distributions of red giant stars with stellar isochrones, and we intercompare the galaxies' halo populations,
noting that their total absolute V magnitudes cover the range from about –21.5 to –17.5. In the future, we plan to model the
stellar metallicity distributions with the aim to constrain chemical enrichment scenarios, a step towards unravelling the
evolutionary history of elliptical and lenticular galaxies.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
OASIS observations obtained at the Canada–France–Hawaii Telescope for the spiral galaxies NGC 4900 and NGC 5430 produce one spectrum for each 0.41″ element of the 11″ × 15″ field of view. This allows for the spatial characterisation of the different stellar populations. From these observations we study the young (10 Myr) and older stellar populations using evolutionary synthesis codes. Based on the gas emission lines, we find that the young populations are located in relatively small regions and dominate the integrated flux. In NGC 4900, the young populations are distributed in a bar-like structure featuring a hole near the position of the galaxy’s centre. The young stellar populations of NGC 5430 form a nuclear ring and two patches at the base of the spiral arms. Based on Mg2 and FeI absorption lines, we find that in both galaxies, the young stars are superimposed on a relatively homogenous population of a few Gyr. 相似文献
14.
We present broad bandR and narrow band Hα emission line images of a sample of optically selected starburst galaxies from the Markarian lists. The
emission line morphology is studied and global properties like luminosities, equivalent widths and star formation rates are
derived. The radial distribution of Ha flux and the EW are determined using concentric aperture photometry on the emission
line and the continuum images. Ha flux is generally found to peak in the nuclear region and fall off outwards. The EW is found
to peak off-center in most of the cases implying that though the intensity of emission is maximum at the nucleus, the star
formation activity relative to the underlying continuum often peaks away from the center in Markarian starburst galaxies. 相似文献
15.
We have taken the case of a circular Hα filament observed on May 9,1979 erupting into a double-ribbon flare associated with
a non-spot region. The plage motions are responsible for the filament reorientation and, here as a special case, wherein the
filament attains a clear circular shape before the onset of a flare. We conclude that the change in the orientation of the
Hα filament marks the instability giving rise to the flare. 相似文献
16.
Six subclusters in the Coma cluster have been selected on the basis of a hierarchical clustering method that takes the gravitational
interaction among galaxies into account. Of these, 3 central subclusters around the galaxies NGC 4889, NGC 4874, and NGC 4839
have been singled out. We have used the objective statistical criterion applied by Vennik and Anosova in studies of close
groups of galaxies to evaluate each member included in a subcluster with a high probability. Galaxies with a significant deficit
of hydrogen HI, including objects from the Bravo-Alfaro list, have been identified with members of the subclusters, with the
greatest number of them in the subclusters around NGC 4874 and NGC 4839. A quantitative estimate of the hydrogen deficit using
the HI index in the RCG3 catalog reveals a statistically significant excess value for those galaxies that are members of the
subclusters compared to galaxies with a hydrogen deficit in the overall Coma cluster field. A substantial number of the spiral
galaxies with a hydrogen deficit in the subclusters turned out to be radio galaxies as well.
__________
Translated from Astrofizika, Vol. 48, No. 4, pp. 515–528 (November 2005). 相似文献
17.
Isaura Fuentes-Carrera Philippe Amram Margarita Rosado 《Astrophysics and Space Science》2002,281(1-2):411-414
We present Hα scanning Fabry-Perot observations of the interacting galaxy pair NGC 3893/96 (Kar 302), an M51-type galaxy pair.
The velocity field and rotation curve of the main galaxy (NGC 3893) were derived. These show the galaxy follows a rather axisymmetric
behaviour. Together with HI observations, several mass models were adjusted in order to study the nature of the dark halo
as well as the mass-to-light ratio of the galaxy. We find that in order to constrain these models, it is important to have
a high resolution Hα rotation curve for the inner parts of the galaxy.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
18.
The probabilistic nature of the IMF in stellar systems implies that clusters of the same mass and age do not present the same
unique values of their observed parameters. Instead they follow a distribution. We address the study of such distributions
in terms of their confidence limits that can be obtained by evolutionary synthesis models. These confidence limits can be
understood as the inherent uncertainties of synthesis models. We will compare such confidence limits arising from the discreteness
of the number of stars obtained with Monte Carlo simulations with the dispersion resulting from an analytical formalism. We
give some examples of the effects on the kinetic energy, V–K, EW(Hβ) and multiwavelength continuum.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
19.
We present and interpret observations of the preflare phase of the eruptive flare of 15 November, 1991 in NOAA AR 6919. New
flux emerged in this region, indicated by arch filaments in Hα and increasing vertical flux in vector magnetograms. With increasing
frequency before the eruption, transient dark Hα fibrils were observed that crossed Hα bright plage and the magnetic inversion
line to extend from the region of flux emergence to the filament, whose eruption was associated with the flare. These crossing
fibrils were dynamic, and were often associated with sites of propagating torsional motion. These sites propagated from the
region of flux emergence into the filament flux system. We interpret these morphological and dynamic features in terms of
relaxation after magnetic reconnection episodes which create longer field lines within the filament flux system, as envisioned
in the tether cutting model, and transfer twist to it, as well.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005086108043 相似文献
20.
We present multiwavelength observations of a large-amplitude oscillation of a polar-crown filament on 15 October 2002, which
has been reported by Isobe and Tripathi (Astron. Astrophys.
449, L17, 2006). The oscillation occurred during the slow rise (≈1 km s−1) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption
were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than
a propagating wave. The amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about
5 km s−1 and 15 000 km, respectively. The period of oscillation was about two hours and did not change significantly during the oscillation.
The oscillation was also observed in Hα by the Flare Monitoring Telescope at the Hida Observatory. We determine the three-dimensional
motion of the oscillation from the Hα wing images. The maximum line-of-sight velocity was estimated to be a few tens of kilometers
per second, although the uncertainty is large owing to the lack of line-profile information. Furthermore, we also identified
the spatial displacement of the oscillation in 17-GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament
oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was
evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We
also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in
the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium
and oscillated. 相似文献