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1.
We present time-resolved spectroscopy of the soft X-ray transient XTE J2123–058 in outburst. A useful spectral coverage of 3700–6700 Å was achieved spanning two orbits of the binary, with single-epoch coverage extending to ∼9000 Å. The optical spectrum approximates a steep blue power law, consistent with emission on the Rayleigh–Jeans tail of a hot blackbody spectrum. The strongest spectral lines are He  ii 4686 Å and C  iii /N  iii 4640 Å (Bowen blend) in emission. Their relative strengths suggest that XTE J2123–058 was formed in the Galactic plane, not in the halo. Other weak emission lines of He  ii and C  iv are present, and Balmer lines show a complex structure, blended with He  ii . He  ii 4686-Å profiles show a complex multiple S-wave structure, with the strongest component appearing at low velocities in the lower-left quadrant of a Doppler tomogram. H α shows transient absorption between phases 0.35 and 0.55. Both of these effects appear to be analogous to similar behaviour in SW Sex type cataclysmic variables. We therefore consider whether the spectral line behaviour of XTE J2123–058 can be explained by the same models invoked for those systems.  相似文献   

2.
The quality of astronomical spectroscopic data now available is so high that interpretation and analysis are often limited by the uncertainties of the laboratory data base. In particular, the limit with which space–time variations in the fine structure constant α can be constrained using quasar spectra depends on the availability of more accurate laboratory rest wavelengths. We recently measured some transitions in magnesium by high-resolution Fourier transform spectroscopy for this purpose, and we now report measurements on some ultraviolet resonance lines of Zn  ii (2062 and 2026 Å), Cr  ii (2066, 2062 and 2056 Å) and Ni  ii (1751, 1741, 1709 and 1703 Å). Apart from the last line, which is very weak, the uncertainty of these measurements is 0.002 cm−1 (0.08 må) for the lines around 2000 Å and 0.004 cm−1 (0.12 må) for the lines around 1700 Å.  相似文献   

3.
We present spectra of six type 1 and two type 2 Seyfert galaxies, a starburst galaxy and a compact narrow-line radio galaxy, taken in two spectral ranges centred around the near-infrared Ca  ii triplet (∼8600 Å), and the Mgb stellar feature at 5180 Å. We measured the equivalent widths (EWs) of these features and the Fe52 and Fe53 spectral indices.
We found that the strength of the infrared Ca  ii triplet (CaT) in type 1 Seyfert galaxies with prominent central point sources is larger than what would be expected from the observed strength of the blue indices. This could be explained by the presence of red supergiants in the nuclei of Seyfert 1 galaxies. On the other hand, the blue indices of these galaxies could also be diluted by the strong Fe  ii multiplets that can be seen in their spectra.
We have also measured the stellar‐ and gas-velocity dispersions of the galaxies in the sample. The stellar velocity dispersions were measured using both the Mgb and CaT stellar features. The velocity dispersion of the gas in the narrow-line region (NLR) was measured using the strong emission lines [O  iii ] λλ 5007, 4959 and [S  iii ] λ 9069. We compare the gas- and star-velocity dispersions and find that the magnitudes of both are correlated in Seyfert galaxies.
Most of the Seyfert 1 galaxies that we observe have stellar‐velocity dispersions somewhat greater than that of the gas in the NLR.  相似文献   

4.
An inspection of a GHRS/ HST spectrum of the symbiotic star RR Telescopii reveals the presence of the [Al  ii ] 3s21S – 3s3p 3P2 line at a vacuum wavelength of 2661.06±0.08 Å, 8.89±0.08 Å away from the Al  ii ] 3s21S – 3s3p 3P1 intercombination transition at 2669.95 Å, in good agreement with the theoretical prediction of Δ λ =8.80 Å. We also find that the Al  ii ] line profile is asymmetric, showing a strong low-density component with a weak high-density wing, redshifted by 30 km s−1, in agreement with the findings of Schild & Schmid, which were based on optical observations. Our measurement of the emission-line ratio R I (2661.06 Å)/ I (2669.95 Å)=0.027±0.003 implies log  N e=5.8±0.2, in good agreement with the densities found from other ions, such as Si  iii . These results provide strong evidence that we have detected the [Al  ii ] line, the first time (to our knowledge) that this feature has been reliably identified in an astrophysical or laboratory spectrum.  相似文献   

5.
The time sequence of 105 spectra covering one full orbital period of AA Dor has been analysed. Direct determination of   V  sin  i   for the sdOB component from 97 spectra outside of the eclipse for the lines Mg  ii 4481 Å and Si  iv 4089 Å clearly indicated a substantially smaller value than estimated before. Detailed modelling of line-profile variations for eight spectra during the eclipse for the Mg  ii 4481 Å line, combined with the out-of-eclipse fits, gave   V  sin  i = 31.8 ± 1.8 km s−1  . The previous determinations of   V  sin  i   , based on the He  ii 4686 Å line, appear to be invalid because of the large natural broadening of the line. With the assumption of the solid-body, synchronous rotation of the sdOB primary, the measured values of the semi-amplitude K 1 and   V  sin  i   lead to the mass ratio   q = 0.213 ± 0.013  which in turn gives K 2 and thus the masses and radii of both components. The sdOB component appears to be less massive than assumed before,   M 1= 0.25 ± 0.05 M⊙  , but the secondary has its mass–radius parameters close to theoretically predicted for a brown dwarf,   M 2= 0.054 ± 0.010 M⊙  and   R 2= 0.089 ± 0.005 R⊙  . Our results do not agree with the recent determination of Vŭcković et al. based on a K 2 estimate from line-profile asymmetries.  相似文献   

6.
A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the He  ii λ 4686 Å (primary component) and He  i λ 4471 Å (secondary component) absorption lines yield semi-amplitudes of 133±2 and 314±2 km s−1 for each binary component, resulting in minimum masses of 31 and 13 M⊙ ( q =0.42) . We also confirm for the binary components the spectral classification of O3 V+ O8 V previously assigned. Assuming for the O8 V component a 'normal' mass of 22–25 M⊙ we would derive for the primary O3 V a mass of 'only' 52–60 M⊙ and an inclination of about 55° for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185±16 yr using all available radial velocity data sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage are also discussed.  相似文献   

7.
This is the initial paper in a series presenting the first optical detections and subsequent follow-up spectroscopy of known southern Galactic supernova remnants (SNRs) previously discovered in the radio. These new detections come from the Anglo-Australian Observatory (AAO)/United Kingdom Schmidt Telescope Hα survey of the southern Galactic plane which has opened up fresh opportunities to study Galactic remnants. Here, we present the first optical imaging and follow-up spectra of Galactic SNR G279.0+1.1 where a series of 14 small-scale fragmented groups of Hα filaments have been discovered in a     area centred on G279.0+1.1. Individually they are somewhat inconspicuous but collectively they are completely enclosed within the overall radio contours of this known SNR. Three of these filamentary groupings are particularly prominent and optical spectra have been obtained across two of them. Their morphological structure and spectral characteristics are typical of optically detected SNR filaments. A very strong [S  ii ] emission relative to Hα has been detected with  [S  ii ]/Hα > 0.7  and 1.1, confirming strong, shock-heated emission. This is sufficient to classify these filaments in the likely SNR domain and therefore indicating a direct connection with the radio remnant. Other typical SNR emission lines such as [O  ii ] at 3727 Å, Hβ, [O  iii ] at 4959 and 5007 Å, Hα and [N  ii ] at 6548 and 6584 Å were also detected, lending strong support to an SNR origin of these optical filaments. The value and insights that these optical data can provide for known remnants are discussed along with their relevance to the Galactic nitrogen abundance. A serendipitous discovery of an adjacent H  ii region is also briefly described.  相似文献   

8.
We present spectra of six luminous quasars at   z ∼ 2  , covering rest wavelengths 1600−3200 Å. The fluxes of the UV Fe  ii emission lines and Mg  ii λ2798 doublet, the line widths of Mg  ii and the 3000 Å luminosity were obtained from the spectra. These quantities were compared with those of low-redshift quasars at   z = 0.06–0.55  studied by Tsuzuki et al. In a plot of the Fe  ii (UV)/Mg  ii flux ratio as a function of the central black hole mass, Fe  ii (UV)/Mg  ii in our   z ∼ 2  quasars is systematically greater than in the low-redshift quasars. We confirmed that luminosity is not responsible for this excess. It is unclear whether this excess is caused by rich Fe abundance at   z ∼ 2  over low-redshift or by non-abundance effects such as high gas density, strong radiation field and high microturbulent velocity.  相似文献   

9.
We present the stellar and gas kinematics of a sample of 18 nearby late-type spiral galaxies (Hubble types ranging from Sb to Sd), observed with the integral-field spectrograph SAURON at the 4.2-m William Herschel Telescope. SAURON covers the spectral range 4800–5380 Å, allowing us to measure the Hβ, Fe, Mg b absorption features and the emission in the Hβ line and the  [O  iii ]λλ4959, 5007 Å  and  [N  i ]λλ5198, 5200 Å  doublets over a  33 × 41-arcsec2  field of view. The maps cover the nuclear region of these late-type galaxies and in all cases include the entire bulge. In many cases the stellar kinematics suggests the presence of a cold inner region, as visible from a central drop in the stellar velocity dispersion. The ionized gas is almost ubiquitous and behaves in a complicated fashion: the gas velocity fields often display more features than the stellar ones, including wiggles in the zero-velocity lines, irregular distributions, ring-like structures. The line ratio [O  iii ]/Hβ often takes on low values over most of the field, probably indicating a wide-spread star formation.  相似文献   

10.
The spectrum of the normal Type Ia SN 1990N observed very early on (14 days before B maximum) was analysed by Fisher et al., who showed that the large width and the unusual profile of the strong line near 6000 Å can be reproduced if the line is assumed to be due to C  ii 6578, 6583 Å and if carbon is located in a high-velocity shell. This line is one of the characterizing features of SNe Ia, and is usually thought to be due to Si  ii . A Monte Carlo spectrum synthesis code is used to investigate this suggestion further. The result is that if a standard explosion model is used, the mass enclosed in the shell at the required high velocity (25 000–35 000 km s−1) is too small to give rise to a strong C  ii line. At the same time, removing silicon has a negative effect on the synthetic spectrum at other wavelengths, and removing carbon from the lower velocity regions near the photosphere makes it difficult to reproduce two weak lines which are naturally explained as C  ii , one of them being the line which Fisher et al. suggested is responsible for the strong 6000-Å feature. However, synthetic spectra confirm that although Si  ii can reproduce most of the observed 6000-Å line, the red wing of the line extends too far to be compatible with a Si  ii origin, and that the flat bottom of the line is also not easy to reproduce. The best fit is obtained for a normal SN Ia abundance mix at velocities near the photosphere (15 500–19 000 km s−1) and an outer carbon–silicon shell beyond 20 000 km s−1. This suggests that mixing is not complete in the outer ejecta of an SN Ia. Observations at even earlier epochs might reveal to what extent a carbon shell is unmixed.  相似文献   

11.
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12.
We present the results of a search for strong H α emission line galaxies (rest frame equivalent widths greater than 50 Å) in the z ≈0.23 cluster Abell 2390. The survey contains 1189 galaxies over 270 arcmin2, and is 50 per cent complete at M r ≈−17.5+5 log  h . The fraction of galaxies in which H α is detected at the 2 σ level rises from 0.0 in the central regions (excluding the cD galaxy) to 12.5±8 per cent at R 200. For 165 of the galaxies in our catalogue, we compare the H α equivalent widths with their [O  ii ] λ 3727 equivalent widths, from the Canadian Network for Observational Cosmology (CNOC1) spectra. The fraction of strong H α emission line galaxies is consistent with the fraction of strong [O  ii ] emission galaxies in the CNOC1 sample: only 2±1 per cent have no detectable [O  ii ] emission and yet significant (>2 σ ) H α equivalent widths. Dust obscuration, non-thermal ionization, and aperture effects are all likely to contribute to this non-correspondence of emission lines. We identify six spectroscopically 'secure' k+a galaxies [ W 0(O  ii )<5 Å and W 0(H δ )≳5 Å]; at least two of these show strong signs in H α of star formation in regions that are covered by the slit from which the spectra were obtained. Thus, some fraction of galaxies classified as k+a based on spectra shortward of 6000 Å are likely to be undergoing significant star formation. These results are consistent with a 'strangulation' model for cluster galaxy evolution, in which star formation in cluster galaxies is gradually decreased, and is neither enhanced nor abruptly terminated by the cluster environment.  相似文献   

13.
We present a study of optical spectra of the Wolf–Rayet star AzV 336a (=SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double-lined WN+O6 spectroscopic binary with an orbital period of 19.56 d. The radial velocities of the He absorption lines of the O6 component and the strong He  ii emission at λ 4686 Å of the WN component describe anti-phased orbital motions. However, they show a small phase shift of ∼1 d. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of He  ii emission is twice that of the absorption lines. The binary components have fairly high minimum masses, ∼18 and 34 M⊙ for the WN and O6 components, respectively.  相似文献   

14.
We have used extensive libraries of model and empirical galaxy spectra [assembled, respectively, from the population synthesis code of Bruzual and Charlot and the fourth data release of the Sloan Digital Sky Survey (SDSS)] to interpret some puzzling features seen in the spectra of high-redshift star-forming galaxies. We show that a stellar He  ii  λ1640 emission line, produced in the expanding atmospheres of Of and Wolf–Rayet stars, should be detectable with an equivalent width of 0.5–1.5 Å in the integrated spectra of star-forming galaxies, provided the metallicity is greater than about half solar. Our models reproduce the strength of the He  ii  λ1640 line measured in the spectra of Lyman-break galaxies for established values of their metallicities. With better empirical calibrations in local galaxies, this spectral feature has the potential of becoming a useful diagnostic of massive star winds at high, as well as low redshifts.
We also uncover a relationship in SDSS galaxies between their location in the [O  iii ]/Hβ versus [N  ii ]/Hα diagnostic diagram (the BPT diagram) and their excess specific star formation rate relative to galaxies of similar mass. We infer that an elevated ionization parameter U is at the root of this effect, and propose that this is also the cause of the offset of high-redshift star-forming galaxies in the BPT diagram compared to local ones. We further speculate that higher electron densities and escape fractions of hydrogen ionizing photons may be the factors responsible for the systematically higher values of U in the H  ii regions of high-redshift galaxies. The impact of such differences on abundance determinations from strong nebular lines are considered and found to be relatively minor.  相似文献   

15.
Deep long-slit spectroscopic data are presented for a sample of 14 3CR radio galaxies at redshift z ∼1, previously studied in detail using the Hubble Space Telescope , the Very Large Array, and the UK Infrared Telescope (UKIRT). Analysis of the [O  ii ] 3727 emission-line structures at ∼5 Å spectral resolution is carried out to derive the kinematic properties of the emission-line gas. In line with previous lower resolution studies, a wide variety of kinematics are seen, from gas consistent with a mean rotational motion through to complex structures with velocity dispersions exceeding 1000 km s −1. The data confirm the presence of a high-velocity gas component in 3C 265 and detached emission-line systems in 3C 356 and 3C 441, and show for the first time that the emission-line gas in the central regions of 3C 324 is composed of two kinematically distinct components. Emission-line fluxes and the colour of the continuum emission are determined down to unprecedentedly low observed wavelengths, λ <3500 Å, sufficiently short that any contribution of an evolved stellar population is negligible. An accompanying paper investigates the variation in the emission-line ratios and velocity structures within the sample, and draws conclusions as to the origin of the ionization and kinematics of these galaxies.  相似文献   

16.
We present CCD photometry of red supergiant long-period variables (LPVs) in the Per OB1 association, the Large Magellanic Cloud (LMC) and M33. The photometry was obtained in the Kron–Cousins R and I bandpasses and in a narrow bandpass ( λ 0=8250 Å, FWHM=300 Å) chosen to avoid TiO bands in the spectral energy distribution of the LPVs. Because the strength of the TiO bands varies greatly with temperature, which varies with the phase of an LPV, avoiding TiO reduces the amplitude of the photometric variations seen in LPVs. The result is a lower dispersion and a well defined period–luminosity (PL) relation.
For the LMC sample we find an rms dispersion of 0.27 mag in the narrow-band PL relation and slightly larger dispersions for the LPVs in Per OB1 and M33. This dispersion is comparable to that of the Cepheid PL relation at similar wavelengths. Adopting a distance modulus of 18.5±0.1 mag for the LMC, we obtain distance moduli of 11.68±0.15 mag for Per OB1 and 24.85±0.13 mag for M33. These distances agree well with those based on main sequence fitting for Per OB1 and the Cepheid distance for M33. Since LPVs are ∼ 5 times more common than Cepheids and have a well defined PL relation, LPVs provide a promising method for estimating Galactic and extra galactic distances.  相似文献   

17.
We report the results of spectroscopic observations of eight southern polar-ring galaxies (PRGs), in the wavelength range 5900–7300 Å. We find that five out of eight galaxies contain LINERs or Sy nuclei. Taking into consideration all PRGs with available spectral data, we estimate that about half of all PRGs and PRG candidates have either LINER or Seyfert nuclei. The observed widths of the [N  ii ] λ 6583 line in the nuclei of early-type PRGs follow the linewidth–absolute luminosity relation for normal E/S0 galaxies. We found that one of the observed galaxies – ESO 576-G69 – is a new kinematically-confirmed polar-ring galaxy with a spiral host.  相似文献   

18.
We present polarimetric and spectroscopic observations of the ROSAT source RX J1141.3−6410, recently identified as a polar. The detection of circular polarization variations, with an amplitude of 10 per cent, over a 3.16-h period confirms that the system is a polar (AM Herculis star). Supporting evidence comes from the nature of the emission lines and their radial velocity variability. In addition, we observe continuum slope changes in the far-red spectral region (∼6000–8200 Å), indicative of phase dependent cyclotron emission. Polarimetric modelling at two wavelengths establishes RX J1141.3−6410 as a single-pole system, with i ∼ β ∼70°. The accretion region is extended in magnetic longitude, and is totally self-occulted for ∼25 per cent of the orbit. The radial velocity curves derived from the emission lines show a phasing with maximum blueshift occurring with Δ φ ∼0.05 of maximum intensity and circular polarisation. In addition, the broader component of the lines exhibit a substantial radial velocity phase shift with respect to the narrower component, in the sense that the broad component preceeds the narrow. This can be readily understood if the narrower component is principally a result of orbital motion of the stream material and the broad component mainly a result of streaming motion near the coupling region. The phasing of the Ca  ii near-infrared line radial velocities also supports this general picture.  相似文献   

19.
We present a mosaic image of the 1.4-GHz radio continuum emission from the Large Magellanic Cloud (LMC) observed with the Australia Telescope Compact Array (ATCA) and the Parkes Telescope. The mosaic covers     with an angular resolution of 40 arcsec, corresponding to a spatial scale of ∼10 pc in the LMC. The final image is suitable for studying emission on all scales between 40 arcsec and the surveyed area. In this paper, we discuss (i) the characteristics of the LMC's diffuse and compact radio continuum emission, (ii) the fraction of the emission produced by thermal processes and the implied star formation rate in the LMC and (iii) variations in the radio spectral index across the LMC. Two non-standard reduction techniques that we used to process the ATCA visibility data may be of interest for future wide-field radio continuum surveys. The data are open to the astronomical community and should be a rich resource for studies of individual objects such as supernova remnants, H  ii regions and planetary nebulae as well as extended features such as the diffuse emission from synchrotron radiation.  相似文献   

20.
New fully relativistic calculations of radiative rates and electron impact excitation cross-sections for Fe  xvi are used to determine theoretical emission-line ratios applicable to the 251–361 and 32–77 Å portions of the extreme-ultraviolet (EUV) and soft X-ray spectral regions, respectively. A comparison of the EUV results with observations from the Solar Extreme-Ultraviolet Research Telescope and Spectrograph (SERTS) reveals excellent agreement between theory and experiment. However, for emission lines in the 32–49 Å portion of the soft X-ray spectral region, there are large discrepancies between theory and measurement for both a solar flare spectrum obtained with the X-Ray Spectrometer/Spectrograph Telescope (XSST) and for observations of Capella from the Low-Energy Transmission Grating Spectrometer (LETGS) on the Chandra X-ray Observatory . These are probably due to blending in the solar flare and Capella data from both first-order lines and from shorter wavelength transitions detected in second and third order. By contrast, there is very good agreement between our theoretical results and the XSST and LETGS observations in the 50–77 Å wavelength range, contrary to previous results. In particular, there is no evidence that the Fe  xvi emission from the XSST flare arises from plasma at a much higher temperature than that expected for Fe  xvi in ionization equilibrium, as suggested by earlier work.  相似文献   

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