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1.
From high-resolution spectra a non-local thermodynamic equilibrium analysis of the Mg  ii 4481.2-Å  feature is implemented for 52 early and medium local B stars on the main sequence (MS). The influence of the neighbouring line Al  iii 4479.9-Å  is considered. The magnesium abundance is determined; it is found that  log ɛ(Mg) = 7.67 ± 0.21  on average. It is shown that uncertainties in the microturbulent parameter Vt are the main source of errors in  log ɛ(Mg)  . When using 36 stars with the most reliable Vt values derived from O  ii and N  ii lines, we obtain the mean abundance  log ɛ(Mg) = 7.59 ± 0.15  . The latter value is precisely confirmed for several hot B stars from an analysis of the Mg  ii 7877-Å  weak line. The derived abundance  log ɛ(Mg) = 7.59 ± 0.15  is in excellent agreement with the solar magnesium abundance  log ɛ⊙ (Mg) = 7.55 ± 0.02  , as well as with the proto-Sun abundance  log ɛ ps (Mg) = 7.62 ± 0.02  . Thus, it is confirmed that the Sun and the B-type MS stars in our neighbourhood have the same metallicity.  相似文献   

2.
Charge-coupled device (CCD) photometry in the Johnson V , Kron–Cousins I and Washington CMT 1 systems is presented in the field of the poorly known open cluster NGC 2627. Four independent Washington abundance indices yield a mean cluster metallicity of  [Fe/H]=−0.12 ± 0.08  , which is compatible with the existence of a radial gradient in the Galactic disc. The resultant colour–magnitude diagrams indicate that the cluster is an intermediate-age object of 1.4 Gyr. Based on the best fits of the Geneva group's isochrones to the ( V , V − I ) and  ( T 1, C − T 1)  diagrams, we estimate   E ( V − I ) = 0.25 ± 0.05  and   V − MV = 11.80 ± 0.25  for  log  t = 9.15  , and   E ( C − T 1) = 0.23 ± 0.07  and   T 1− M T 1= 11.85 ± 0.25  for  log  t = 9.10  , respectively, assuming solar metal content. The derived reddening value   E ( C − T 1)  implies   E ( B − V ) = 0.12 ± 0.07  and a distance from the Sun of  2.0 ± 0.4 kpc  . Using the WEBDA data base and the available literature, we re-examined the overall properties of all the open clusters with ages between 0.6 and 2.5 Gyr. We identified peaks of cluster formation at 0.7–0.8, 1.0–1.1, 1.6–1.7 and 2.0–2.1 Gyr, separated by relative quiescent epochs of ∼0.2–0.3 Gyr. We also estimated a radial abundance gradient of  −0.08 ± 0.02  , which is consistent with the most recent determinations for the Galactic disc, but no clear evidence for a gradient perpendicular to the Galactic plane is found.  相似文献   

3.
To study the kinematics of O-B5 giant stars (luminosity class III), 290 non-Gould belt stars with proper motions taken from the Hipparcos catalogue are used, of which 107 have radial velocities taken from other sources. Semidefinite programming solves for the kinematical parameters and the coefficients of the velocity ellipsoid. The condition that both solutions must yield the same solar velocity is enforced. The results obtained are reasonable: solar velocity of 13.83 ± 0.17 km s−1; Oort's constants, in units of km s−1 kpc−1, A = 16.08 ± 0.72 and   B =−10.74 ± 0.65,  implying a rotational velocity of 228.0 ± 21.4 km s−1 if we take the distance to the Galactic Centre as 8.5 ± 1.1 kpc; velocity dispersions, in units of km s−1, of  σ x = 32.44 ± 5.04, σ y = 26.16 ± 2.75, σ z = 18.71 ± 2.39  with a vertex deviation of      相似文献   

4.
We report the discovery of a 7.3 M J exoplanet WASP-14b, one of the most massive transiting exoplanets observed to date. The planet orbits the 10th-magnitude F5V star USNO-B1 11118−0262485 with a period of 2.243 752 d and orbital eccentricity   e = 0.09  . A simultaneous fit of the transit light curve and radial velocity measurements yields a planetary mass of 7.3 ± 0.5 M J and a radius of 1.28 ± 0.08 R J. This leads to a mean density of about 4.6 g cm−3 making it the densest transiting exoplanets yet found at an orbital period less than 3 d. We estimate this system to be at a distance of  160 ± 20  pc. Spectral analysis of the host star reveals a temperature of  6475 ± 100 K, log  g = 4.07  cm s−2 and   v sin  i = 4.9 ± 1.0  km s−1, and also a high lithium abundance,  log  N (Li) = 2.84 ± 0.05  . The stellar density, effective temperature and rotation rate suggest an age for the system of about 0.5–1.0 Gyr.  相似文献   

5.
We have discovered that the spectrum of the well-known dwarf nova EM Cyg is contaminated by light from a K25V star (in addition to the K-type mass donor star). The K25V star contributes approximately 16 per cent of the light from the system and if not taken into account has a considerable effect upon radial velocity measurements of the mass donor star. We obtain a new radial velocity amplitude for the mass donor star of K 2=202±3 km s1, compared with the value of K 2=135±3 km s1 obtained in Stover, Robinson & Nather's classic study of EM Cyg. The revised value of the amplitude, combined with a measurement of rotational broadening of the mass donor, v  sin  i =140±6 km s1, leads to a new mass ratio of q M 2 M 1=0.88±0.05. This solves a long-standing problem with EM Cyg, because Stover et al.'s measurements indicated a mass ratio q >1, a value that should have led to dynamically unstable mass transfer for the secondary mass deduced by Stover et al. The revised value of the mass ratio, combined with the orbital inclination i =67±2°, leads to masses of 0.99±0.12 M and 1.12±0.08 M for the mass donor and white dwarf respectively. The mass donor is evolved, because it has a later spectral type (K3) than its mass would imply.
We discuss whether the K star could be physically associated with EM Cyg or not, and present the results of the spectroscopic study.  相似文献   

6.
In a previous paper by the present authors the theory of Anstee and O'Mara for the broadening of spectral lines of neutral atoms by collisions with hydrogen atoms was extended to singly ionized atoms. In this paper we apply the method to the resonance and triplet lines of ionized strontium, the infrared triplet of ionized barium, and the resonance lines of ionized beryllium. Analysis of five lines of ionized strontium, previously regarded as too strong for an abundance analysis, and two lines of neutral strontium results in a solar abundance of strontium of log( N Sr N H)+12=2.92±0.05, which is entirely consistent with the meteoritic value.  相似文献   

7.
High-resolution spectroscopic observations around the Hα line of the binary star QX Cas covering the whole orbital period are presented. Our radial velocity solution, the first ever determined, requires an eccentric orbit with the following orbital parameters: eccentricity,   e = 0.22 ± 0.01  ; longitude of periastron,  ω= 45°± 5°  ; semi-amplitudes of the radial velocity curves of the primary and secondary stars,   K 1 sin  i = 125.8 ± 0.9 km s−1  and   K 2 sin  i = 144.8 ± 1.1 km s−1  ; gamma velocity,   V 0= 65.1 ± 0.5 km s−1  ; and mass ratio,   q = 0.869 ± 0.013  . The corresponding lower limits of the masses of the components and their separation are         , and   a sin  i = 31.34 ± 0.48 R⊙  .  相似文献   

8.
We use accurate absolute proper motions and Two-Micron All-Sky Survey   Ks   -band apparent magnitudes for 364 Galactic RR Lyrae variables to determine the kinematical parameters of the Galactic RR Lyrae population and constrain the zero-point of the   Ks   -band period–luminosity relation for these stars via statistical parallax. We find the mean velocities of the halo- and thick-disc RR Lyrae populations in the solar neighbourhood to be  [ U 0(Halo), V 0(Halo), W 0(Halo)]= (−12 ± 10, −217 ± 9, −6 ± 6) km s−1  and  [ U 0(Disc), V 0(Disc), W 0(Disc)]= (−15 ± 7, −44 ± 7, −25 ± 5) km s−1  , respectively, and the corresponding components of the velocity-dispersion ellipsoids,  [σ VR (Halo), σ V θ(Halo), σ W (Halo)]= (167 ± 9, 86 ± 6, 78 ± 5) km s−1  and  [σ VR (Disc), σ V θ(Disc), σ W (Disc)]= (55 ± 7, 44 ± 6, 30 ± 4) km s−1  , respectively. The fraction of thick-disc stars is estimated at  0.25 ± 0.03  . The corrected infrared period–luminosity relation is     , implying a Large Magellanic Cloud (LMC) distance modulus of  18.27 ± 0.08  and a solar Galactocentric distance of  7.58 ± 0.40 kpc  . Our results suggest no or slightly prograde rotation for the population of halo RR Lyraes in the Milky Way.  相似文献   

9.
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   

10.
Simultaneous spectroscopic and photometric observations of the Z Cam type dwarf nova SY Cancri were used to obtain absolute flux calibrations. A comparison of the photometric calibration with a wide-slit spectrophotometric calibration showed that either method is equally satisfactory. A radial velocity study of the secondary star, made using the far-red Na  i doublet, yielded a semi-amplitude of   K 2= 127 ± 23 km s−1  . Taking the published value of  86 ± 9 km s−1  for K 1 gives a mass ratio of   q = M 2/ M 1= 0.68 ± 0.14  ; this is very different from the value of  1.13 ± 0.35  quoted in the literature. Using the new lower mass ratio, and constraining the mass of the white dwarf to be within reasonable limits, then leads to a mass for the secondary star that is substantially less than would be expected for its orbital period if it satisfied a main-sequence mass–radius relationship. We find a spectral type of M0 that is consistent with that expected for a main-sequence star of the low mass we have found. However, in order to fill its Roche lobe, the secondary must be significantly larger than a main-sequence star of that mass and spectral type. The secondary is definitely not a normal main-sequence star.  相似文献   

11.
Intermediate-resolution (0.5–1 Å) optical spectroscopy of the cataclysmic variable (CV) SY Cnc reveals the spectrum of the donor star. Our data enable us to resolve the orbital motion of the donor and provide a new orbital solution, binary mass ratio and spectral classification. We find that the donor star has spectral-type G8 ± 2 V and orbits the white dwarf with   P = 0.382 3753 ± 0.000 0003  d,   K 2= 88.0 ± 2.9  km s−1 and   V sin  i = 75.5 ± 6.5  km s−1. Our values are significantly different from previous works and lead to   q = M 2/ M 1= 1.18 ± 0.14  . This is one of the highest mass ratios known in a CV and is very robust, because it is based on resolving the rotational broadening over a large number of metallic absorption lines. The donor could be a slightly evolved main sequence or descendant from a massive star which underwent an episode of thermal time-scale mass transfer.  相似文献   

12.
A time-resolved spectroscopic study of V603 Aql (Nova Aquilae 1918) is presented. An orbital period of P orb=01385±00002, consistent with previous results, and a radial velocity semi-amplitude of K =20±3 km s1 are obtained from the radial velocity variations of the H emission line. Similar K values are also found in H , H , and He  i emission lines. Using the measured FWHM of the H line and assuming that the derived semi-amplitude is that of the white dwarf, we deduce a most likely mass ratio of q =0.24±0.05 and stellar masses of M 2=0.29±0.04 M and M 1=1.2±0.2 M for the secondary and primary (the white dwarf) star, respectively. The dynamical solution also indicates a very low orbital inclination, i =13°±2°. We find that the continuum and line variations are modulated with both the positive and the negative superhump periods, indicating that they arise from similar regions of the accretion disc. Moreover, we find, for the first time from spectroscopy, evidence of negative superhumps in addition to the positive superhumps. Positive superhumps are explained within the disc instability model as caused by an eccentric disc surrounding the white dwarf, which is precessing (apsidal advance) because of tidal instabilities, causing the observed positive superhumps. A nodal precession in the accretion disc is currently believed to be the cause of the observed negative superhumps. The low value of q is consistent with the expected value for systems that show superhumps, in accordance with the eccentric disc model. We find no evidence of periodicity associated with the spin period.  相似文献   

13.
Mayall II = G1 is one of the most luminous globular clusters (GCs) known in M31. New deep, high-resolution observations with the Advanced Camera for Surveys on the Hubble Space Telescope are used to provide accurate photometric data to the smallest radii yet. In particular, we present the precise variation of ellipticity and position angle, and of surface brightness for the core of the object. Based on these accurate photometric data, we redetermine the structural parameters of G1 by fitting a single-mass isotropic King model. We derive a core radius,   r c= 0.21 ± 0.01  arcsec (= 0.78 ± 0.04  pc)  , a tidal radius,   r t= 21.8 ± 1.1  arcsec (= 80.7 ± 3.9  pc)  , and a concentration index   c = log ( r t/ r c) = 2.01 ± 0.02  . The central surface brightness is 13.510 mag arcsec−2. We also calculate the half-light radius, at   r h= 1.73 ± 0.07  arcsec (= 6.5 ± 0.3  pc)  . The results show that, within 10 core radii, a King model fits the surface brightness distribution well. We find that this object falls in the same region of the   MV   versus  log   R h  diagram as ω Centauri, M54 and NGC 2419 in the Milky Way. All three of these objects have been claimed to be the stripped cores of now defunct dwarf galaxies. We discuss in detail whether GCs, stripped cores of dwarf spheroidals and normal dwarf galaxies form a continuous distribution in the   MV   versus  log   R h  plane, or if GCs and dwarf spheroidals constitute distinct classes of objects; we present arguments in favour of this latter view.  相似文献   

14.
An automatic Bayesian Kepler periodogram has been developed for identifying and characterizing multiple planetary orbits in precision radial velocity data. The periodogram is powered by a parallel tempering Markov chain Monte Carlo (MCMC) algorithm which is capable of efficiently exploring a multiplanet model parameter space. The periodogram employs an alternative method for converting the time of an observation to true anomaly that enables it to handle much larger data sets without a significant increase in computation time. Improvements in the periodogram and further tests using data from HD 208487 have resulted in the detection of a second planet with a period of 90982−92 d, an eccentricity of 0.370.26−0.20, a semimajor axis of 1.870.13−0.14 au and an M sin  i = 0.45+0.11−0.13 M J. The revised parameters of the first planet are period = 129.8 ± 0.4 d, eccentricity = 0.20 ± 0.09, semimajor axis = 0.51 ± 0.02 au and M sin  i = 0.41 ± 0.05  M J. Particular attention is paid to several methods for calculating the model marginal likelihood which is used to compare the probabilities of models with different numbers of planets.  相似文献   

15.
We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of   K R= 198 ± 5 km s−1  . The rotational velocity of the secondary star in V347 Pup is found to be   v sin  i = 131 ± 5 km s−1  and the system inclination is   i = 840 ± 23  . From these parameters we obtain masses of   M 1= 0.63 ± 0.04 M⊙  for the white dwarf primary and   M 2= 0.52 ± 0.06 M⊙  for the M0.5V secondary star, giving a mass ratio of   q = 0.83 ± 0.05  . On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc.  相似文献   

16.
High-resolution spectroscopic observations around the Hα line and BVRI photometry of the eclipsing short-period RS CVn star UV Leo are presented. The simultaneous light-curve solution and radial velocity-curve solution led to the following values of the global parameters of the binary: temperatures   T 1= 6000 ± 100 K  and   T 2= 5970 ± 20 K  ; masses   M 1= 0.976 ± 0.067 M⊙  and   M 2= 0.931 ± 0.052 M⊙  ; separation   a = 3.716 ± 0.048 R⊙  ; orbital inclination     ; radii   R 1= 1.115 ± 0.052 R⊙  and   R 2= 1.078 ± 0.051 R⊙  ; equatorial velocities   V 1= 98.8 ± 2.3 km s−1  and   V 2= 89.6 ± 2.7 km s−1  . These results lead to the conclusion that the two components of UV Leo are slightly oversized for their masses and lie within the main-sequence band on the mass–radius diagram, close to the isochrone 9 × 1010 yr.  相似文献   

17.
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   

18.
We construct a new sample of ∼1700 solar neighbourhood halo subdwarfs from the Sloan Digital Sky Survey (SDSS), selected using a reduced proper-motion diagram. Radial velocities come from the SDSS spectra and proper motions from the light-motion curve catalogue of Bramich et al. Using a photometric parallax relation to estimate distances gives us the full phase-space coordinates. Typical velocity errors are in the range  30–50 km s−1  . This halo sample is one of the largest constructed to date and the disc contamination is at a level of ≲1 per cent. This enables us to calculate the halo velocity dispersion to excellent accuracy. We find that the velocity dispersion tensor is aligned in spherical polar coordinates and that  (σ r , σφ, σθ) = (143 ± 2, 82 ± 2, 77 ± 2) km s−1  . The stellar halo exhibits no net rotation, although the distribution of   v φ  shows tentative evidence for asymmetry. The kinematics are consistent with a mildly flattened stellar density falling with distance like   r −3.75  .
Using the full phase-space coordinates, we look for signs of kinematic substructure in the stellar halo. We find evidence for four discrete overdensities localized in angular momentum and suggest that they may be possible accretion remnants. The most prominent is the solar neighbourhood stream previously identified by Helmi et al., but the remaining three are new. One of these overdensities is potentially associated with a group of four globular clusters (NGC 5466, NGC 6934, M2 and M13) and raises the possibility that these could have been accreted as part of a much larger progenitor.  相似文献   

19.
We present optical and near-infrared photometry and spectroscopy of the Type Ia SN 2003cg, which exploded in the nearby galaxy NGC 3169. The observations cover a period between −8.5 and +414 d post-maximum. SN 2003cg is a normal but highly reddened Type Ia event. Its B magnitude at maximum   B max= 15.94 ± 0.04  and  Δ m 15( B )obs= 1.12 ± 0.04 [Δ m 15( B )intrinsic= 1.25 ± 0.05]  . Allowing   RV   to become a free parameter within the Cardelli et al. extinction law, simultaneous matches to a range of colour curves of normal SNe Ia yielded   E ( B − V ) = 1.33 ± 0.11  , and   RV = 1.80 ± 0.19  . While the value obtained for   RV   is small, such values have been invoked in the past, and may imply a grain size which is small compared with the average value for the local interstellar medium.  相似文献   

20.
We present BVR polarimetric study of the cool active star LO Pegasi (LO Peg) for the first time. LO Peg was found to be highly polarized among the cool active stars. Our observations yield average values of polarization in LO Peg:   PB = 0.387 ± 0.004 per cent, θB= 88°± 1°; PV = 0.351 ± 0.004 per cent, θV= 91°± 1°  and   PR = 0.335 ± 0.003 per cent, θR= 91°± 1°  . Both the degree of polarization and the position angle are found to be variable. The semi-amplitude of the polarization variability in B, V and R bands is found to be  0.18 ± 0.02, 0.13 ± 0.01  and  0.10 ± 0.02  per cent, respectively. We suggest that the levels of polarization observed in LO Peg could be the result of scattering of an anisotropic stellar radiation field by an optically thin circumstellar envelope or scattering of the stellar radiation by prominence-like structures.  相似文献   

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