Fast variability of the outflow in the Z CMa system

High-resolution, time-resolved spectroscopic observations of Z CMa carried out on 1997 January 14–17 are presented. Large night-to-night and hour-to-hour variations in Hα, Hβ and Na i D P Cygni absorptions, as well as an Hβ emission peak, were observed. Variations in the red wings of the hydrogen emission lines were also detected. The high-velocity wide-emission component on the blue side of Hα appeared on January 17. The observations are discussed in the framework of current wind models.     

Hα long-term monitoring of the Be star β Cephei Aa

Papers published in recent years have contributed to resolve the enigma of the hypothetical Be nature of the hot pulsating star β Cephei. This star shows variable emission in the Hα line, typical for Be stars, but its projected rotational velocity is very much lower than the critical limit, contrary to what is expected for a typical Be star. The emission has been attributed to the secondary component of the β Cephei spectroscopic binary system.
In this paper, using both our and archived spectra, we attempt to recover the Hα profile of the secondary component and to analyse its behaviour with time for a long period. To accomplish this task, we first derive the atmospheric parameters of the primary,   T _eff= 24 000 ± 250 K  and  log  g = 3.91 ± 0.10  , and then we use these values to compute its synthetic Hα profile, and finally we reconstruct the secondary's profile disentangling the observed one.
The secondary's Hα profile shows the typical two-peak emission of a Be star with a strong variability. We also analysed the behaviour versus time of some linewidth parameters: equivalent width, ratio of blue to red peak intensities, full width at half-maximum, peak separation and radial velocity of the central depression.
The projected rotational velocity  ( v sin  i )  of the secondary and the dimension of the equatorial surrounding disc have also been estimated.     

Radial velocity study of the roAp star α Circinus

We present results of 548 high-dispersion spectra of the roAp star α Circinus over a five-night period. The pulsational radial velocities measured from the rare-earth elements, Nd iii , Hα and Hβ are easily measured and occur at the photometric period. The amplitude is largest in Nd iii and Hα, is lower in the rare earths and Hβ, and cannot be measured in other metal lines. This behaviour can be understood in terms of an increase of pulsational amplitude with height in the atmosphere coupled with abundance stratification. The radial velocities show a significant variation at the rotational period of 4.463 d and a marginally significant periodicity at a frequency of 8.16 cycle d⁻¹. The latter may be a very low-amplitude δ Scuti pulsation.     

Long-term variability of the Be/X-ray binary A 0535+26 – I. Optical and UV spectroscopy

The results of a 7-yr optical and UV spectroscopic study of the high-mass X-ray binary A 0535+26 are presented. It was found that throughout the period of the observations the line profile of Hα showed considerable variability. A correlation between the equivalent width of Hα and both V -band magnitude and ( B − V ) colour excess was observed, albeit with considerable scatter present in the data set. A giant X-ray flare in early 1994 was accompanied by a fading in optical and infrared photometric bands, and a reduction in the equivalent width of Hα. When the star was observed in 1994 September, it was found to have developed a double-peaked Hα profile, and further observations saw the V/R peak ratio vary cyclically, with a period of ∼1 yr. If this is identified as a global one-armed oscillation, it becomes the shortest period ever observed in a Be star. The accompanying photometric and spectroscopic observations provide a test of any theory seeking to describe the onset and behaviour of such a density wave.     

Structure of the inner regions of the circumstellar gas envelopes around young hot stars. II. The new cycle of spectral activity of the Herbig Ae star HD 31648

The results of the high-resolution long-term spectral monitoring of the Herbig Ae star HD 31648 in the regions of emission Hα line, Na I D resonance lines and OI 7774 lines are presented. We confirmed the conclusion, made in previous papers, that the spectral variability of the star in the region of Hα line have a cyclic character. It is manifested itself as the changing of the equivalent width and intensity of Hα line of the time scale of about 1200d. It is shown, that the stellar wind is non-homogeneous and consists of several components, which are differed each other by their velocities. They are observed as in the H line as in Na I D resonance lines. The component’s parameters are changed during the cycle of stellar activity (in the maximum of activity the velocity and density of the wind are taken the largest values and then they are gradually decreased). The investigation of rapid variability of the He I 5876 line on the time scale of a few hours allows find the correlation between the variability of the blue and the red wings of the line. It points at the connection between the accretion and the outflows. Such connection, in particularly, is predicted by the modeling of the wind from young stars made in the frame of the magneto-centrifugal model, the accordance of which for the HD 31648 was shown in the previous papers. In the present work we confirmed this conclusion on the basis of the new data. We found the weak variability of the stellar brightness (about 0.2m), which is agree with the spectral variability (the brightness of the star becomes lower in the maximum of the activity). These changes are well explained by the process of the dust transfer from CS disk by the stellar wind. This process is likely to be more effective in the maximum of activity. An analysis of the variability of other spectral lines shows the agreement between the changing of the Hα line, the Na I D resonance doublet lines and KI 7698 line. The weak connection between the He I 5876 and the Na I D lines is also found. Since the formation regions of He I 5876 and Na I D lines are essentially different, we can conclude that the phenomena, responsible for the observed cyclic variability, take place in a spacious region of the CS envelope. We believe that the most plausible reason of found cyclic variability is the reconstruction of the inner structure of the CS gas envelope, caused by the presence around the star a low mass companion or planet. __________ Translated from Astrofizika, Vol. 50, No. 4, pp. 565–588 (November 2007).     

Infrared spectroscopy of the Be/X-ray transient A0535+26

We present infrared spectroscopy of the Be/X-ray binary HDE 245770/A0535+26 obtained over the period 1992–1995. The spectra show significant variability, reflecting changes in the circumstellar environment during this time. A reduction in the flux observed in the Paschen series lines between 1993 December and 1994 September correlates with a similar reduction in both the strength of Hα and the optical continuum emission, which can be attributed to a reduction in the emission measure of the disc. A turnover between optically thin and thick emission is seen for both Paschen and Brackett series lines, and allows an estimate of the disc density as ∼10¹² cm⁻³. Echelle spectroscopy reveals strong similarities between the He I 1.008, 2.058 μm, Hα and Paschen series line profiles, suggesting their formation in a similar (and asymmetric) region of the disc. In contrast, the line profile of He I 6678 Å indicates that it is formed at smaller radii than the other transitions.     

Doppler images and chromospheric variability of TWA 17

We present Doppler imaging and a Balmer line analysis of the weak-line T Tauri star TWA 17. Spectra were taken in 2006 with the University College London Echelle Spectrograph on the Anglo-Australian Telescope. Using least-squares deconvolution to improve the effective signal-to-noise ratio, we produced a Doppler map of the surface spot distribution. This shows similar features to maps of other rapidly rotating T Tauri stars, i.e. a polar spot with more spots extending out of it down to the equator.
In addition to the photospheric variability, the chromospheric variability was studied using the Balmer emission. The mean Hα profile has a narrow component consistent with rotational broadening and a broad component extending out to 220 km s⁻¹. The variability in Hα suggests that the chromosphere has at least one slingshot prominence  3 R _*  above the surface.     

Correlated optical/X-ray variability in the high-mass X-ray binary SAX J2103.5+4545

SAX J2103.5+4545 is the Be/X-ray binary (BeX) with the shortest orbital period. It shows extended bright and faint X-ray states that last for a few hundred days. The main objective of this work is to investigate the relationship between the X-ray and optical variability and to characterize the spectral and timing properties of the bright and faint states. We have found a correlation between the spectral and temporal parameters that fit the energy and power spectra. Softer energy spectra correspond to softer power spectra. That is to say, when the energy spectrum is soft, the power at high frequencies is suppressed. We also present the results of our monitoring of the Hα line of the optical counterpart since its discovery in 2003. There is a correlation between the strength and shape of the Hα line, originated in the circumstellar envelope of the massive companion and the X-ray emission from the vicinity of the neutron star. Hα emission, indicative of an equatorial disc around the B-type star, is detected whenever the source is bright in X-rays. When the disc is absent, the X-ray emission decreases significantly. The long-term variability of SAX J2103.5+4545 is characterized by fast episodes of disc loss and subsequent reformation. The time-scales for the loss and reformation of the disc (about 2 yr) are the fastest among BeXs.     

The spectral variations of the O-type runaway supergiant HD 188209

We report spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations of photospheric absorption lines with a possible quasi-period of ∼6.4 d have been detected in high-resolution echelle spectra. Night-to-night variations in the position and strength of the central emission reversal of the H α profile occurring over ill-defined time-scales have been observed. The fundamental parameters of the star are derived using state-of-the-art plane-parallel and unified non-LTE model atmospheres, the latter including the mass-loss rate. The derived helium abundance is moderately enhanced with respect to solar, and the stellar masses are lower than those predicted by the evolutionary models. The binary nature of this star is not suggested either from Hipparcos photometry or from radial velocity curves.     

Balmer absorption variability and the disc wind of V592 Cassiopeiae

We present results from time-series optical spectroscopy of the low-inclination, nova-like cataclysmic variable, V592 Cas. The data span the wavelength range from ∼4000 to 5000  Å, and include Balmer lines (Hβ to Hε) as well as He i and He ii . The Balmer lines are generally characterized by shallow absorption troughs with superimposed narrower central emission components. The absorption troughs are variable on time-scales of at least ∼20 min, but the fluctuations are asymmetric such that they are more dominant on the blueward side of the profile out to ∼−2000 km s⁻¹. Fourier analysis reveals modulation periods for emission radial velocities and absorption changes of ∼0.114 and 0.103 d; we support earlier suggestions that the latter is likely to be 1-day alias of the former, which is essentially the system orbital period. However, there is a phase lag of ∼0.3 between absorption and emission changes. The Balmer absorption changes are compared to the predicted behaviour caused by the (stream overflowing) SW Sex phenomenon. There are several discrepancies in this scenario, including the highly asymmetric nature of blueward changes, the velocity amplitudes, and the phase relation to the emission changes. The role of a disc wind in V592 Cas is also discussed; in particular, with this data set, we cannot rule in or rule out the possibility that axisymmetry of the outflow is broken because it is seated on a warped/tilted inner disc, which is implied by previous evidence for negative superhumps in this system.     

Long-Term Spectral Variability of the Herbig Ae-Star HD 179218

The results of high-resolution long-term spectral monitoring of Herbig Ae star HD 179218 in the region of emission H line and the sodium resonance doublet Na I D are presented. The received data show the existence of short-term variability (about 10 days) and long-term wave-like variability of equivalent width EW, intensity of circumstellar (CS) emission I and parameters of H emission profile. The analysis of these data allows us to suppose the existence of the global variability of parameters of accretion disk.     

Doppler signatures of Hα flares in AE Aquarii

We present high-speed spectrophotometric observations of the Hα emission in the exotic cataclysmic variable AE Aqr. Over 10 000 spectra with a sampling rate of ∼ 6 s were obtained. The well-known 16.5- and 33-s oscillations were not detected in either the continuum or the line, nor were any quasi-periodic oscillations detected. The Hα line shows remarkably complex behaviour, with changes in flux of up to a factor of 3 in a few hours. The line does not act as a single entity — the instantaneous line profile is highly asymmetric and consists of a superposition of emission components that are localized in velocity. We find that during flares the Hα emission is delayed and decays more slowly than the continuum. The Hα variations are not linearly correlated with the continuum variations. Examination of the trailed spectrograms and Doppler tomograms reveals no signatures of an accretion disc, but rather supports the idea that mass is being ejected by a propeller mechanism.     

Latitude distributions and lifetimes of star-spots on G dwarfs in the α Persei cluster

We present a set of maximum-entropy reconstructions of the star-spot distributions on two rapidly rotating G dwarfs in the α Persei cluster, from spectra taken at the William Herschel Telescope on three nights in 1996 October and November. Since these stars are too faint for conventional Doppler imaging, which makes use of only one or a few lines, we take the large number of photospheric metal lines available in an echelle spectrum, and deconvolve them into a single, high signal-to-noise ratio profile. We show that this technique results in a typical multiplex gain of 22.5 in signal-to-noise ratio for a given spectrum, the equivalent of using a single line obtained on a 63-m telescope. The image reconstructions demonstrate that both these stars have cool high-latitude regions or polar crowns, and low-latitude features, in contradiction to the suggestion that only high-latitude spots should be present. Cross-correlation between image reconstructions of He 699, 31 days apart, reveals a lack of correlation between detailed small-scale structures. This places an upper limit for the lifetime of the observed features at less than one month. The Hα profiles are also found to exhibit absorption features indicating the presence of prominence clouds, at or below the corotation radius.     

The Hα echoes of ε Carinae from 1985 to 1997

Spatially resolved, broad Hα line profiles from both the luminous blue variable star ε Carinae (ε Car) and the surrounding filamentary Car II ('Keyhole') nebula, where they have been scattered and reflected by dust, have been observed periodically from 1985 to 1997. The Hα line profiles from ε Car in this 12-yr period show some, albeit not dramatic, changes. The sharp and deep P Cygni-type absorption feature that was observed first in 1985 in the broad, scattered/reflected profiles from the surrounding Keyhole nebula is not present in any of the direct ε Car profiles. This distinctive feature is now shown to be spatially variable over the Keyhole nebula and most prominent along the direction of the axis of the bipolar Homunculus nebula at PA 132°. No evidence of any temporal variability of this sharp feature has been found in 12 yr of monitoring, even from the most well-defined scattering/reflecting cloud along PA 132°.
It is concluded that a 46°-wide cone of light from ε Car is relatively unobscured along the axis of the Homunculus nebula and that this must be the consequence of a dense torus close to the star.     

Repetitive structure in the stellar wind of HD 93843: a normal O-type star

We present the results from a 28-day IUE time-series campaign monitoring the stellar wind of the O5-type giant HD 93843. The principal aim was to study variability in the wind of a star with a normal projected rotation velocity. Systematic changes are identified, amidst continuous line-profile variability, in the absorption troughs of the Si  iv and N  v resonance lines. The patterns observed have characteristic time-scales of several days and are mimicked by fluctuations (of several 100 km s⁻¹) in the blue wings of the saturated C  iv P Cygni profile.   Fourier analysis provides support for the repeatability of wind structures in HD 93843 on a 7.1-d 'period'. Power at this frequency is evident only at intermediate and high velocities (i.e., above ∼0.3 of the terminal velocity). The long modulation time-scale suggests that changes in the star itself probably provide the physical source for triggering the onset of wind structure. Unfortunately the rotational, photometric, pulsational and magnetic properties of HD 93843 are too poorly constrained or known to permit a more detailed interpretation of the 7.1-d wind modulation in terms of potential inhomogeneities at the stellar surface. Nevertheless, our study demonstrates that the incidence of cyclic, possibly regular, stellar-wind variability is not restricted to rapid rotators. Comparisons with other OB stars which have exhibited repetitive wind changes on 'periods' of several days suggest that the time-dependent UV properties of HD 93843 are more akin to those of the O4-type supergiant ζ Puppis.     

Photometric, spectroscopic and polarimetric variability of the weak-emission T Tauri star HD 288313

Photometric observations over three seasons show HD 288313 to be a light variable with a 2.2636-d period. The observed V amplitudes lie in the range of 0.06–0.15 mag. The star showed appreciable changes in the brightness at maximum and minimum of the light curve from season to season. The (   b − y   ) colour did not show any significant variation during the photometric cycle. The light variation appears to be caused by the rotational modulation of stellar flux by cool starspots distributed asymmetrically across the stellar longitudes. The Hα line strength in HD 288313 varied drastically from completely filled-in emission to almost full absorption, that is typical of a normal star of similar spectral type. The Hα equivalent width is found to show a clear rotational modulation only occasionally. Most of the time, chromospheric active regions are distributed well across the stellar longitudes, thereby suppressing obvious rotational modulations. Broad-band linear polarization measurements show HD 288313 to be a short period, low-amplitude polarization variable. The polarization variation is, apparently, rotationally modulated. Dust grain scattering in a non-spherical circumstellar envelope of a star with inhomogeneities in the surface brightness distribution seems to be the mechanism operating in producing the observed polarization.     

Multiwavelength study of the transient X-ray binary IGR J01583+6713

We have investigated multiband optical photometric variability and stability of the Hα line profile of the transient X-ray binary IGR J01583+6713. We set an upper limit of 0.05 mag on photometric variations in the V band over a time-scale of three months. The Hα line is found to consist of non-Gaussian profile and quite stable for a duration of two months. We have identified the spectral type of the companion star to be B2 IVe while the distance to the source is estimated to be ∼4.0 kpc. Along with the optical observations, we have also carried out analysis of X-ray data from three short observations of the source, two with the Swift –XRT and one with the RXTE –PCA. We have detected a variation in the absorption column density, from a value of  22.0 × 10²² cm⁻²  immediately after the outburst down to  2.6 × 10²² cm⁻²  four months afterwards. In the quiescent state, the X-ray absorption is consistent with the optical reddening measurement of   E ( B − V ) = 1.46  mag. From one of the Swift observations, during which the X-ray intensity was higher, we have a possible pulse detection with a period of 469.2 s. For a Be X-ray binary, this indicates an orbital period in the range of 216–561 d for this binary system.     

Time-series Paschen-β spectroscopy of SU Aurigae

We present time-series echelle spectra of the Paβ line of the T Tauri star SU Aur, observed over three consecutive nights. The line shows strong variability (∼10 per cent) over the velocity range 100–420 km s⁻¹ in the red broad absorption component, and weaker variability (∼2 per cent) over the velocity range  −200–0 km s⁻¹  in the blue wing. The variability in the velocity range  −200–0 km s⁻¹  is correlated with that in  200–400 km s⁻¹  , and the variability in these velocity ranges anticorrelates with that in  0–100 km s⁻¹  . The mean spectrum from the second night shows the suggestion of a blueshifted absorption component at about  −150 km s⁻¹  , similar to that found in the Hα and Hβ lines. We find the position of the subpeak in the red absorption component changes steadily with time, and its motion modulates at half the rotational period. We also find that the modulation of the line equivalent width is possibly associated with a half and a third of the rotational period, which is consistent with the surface Doppler images of SU Aur. Radiative transfer models of a rotationally modulated Paβ line, produced in the shock-heated magnetospheric accretion flow, are also presented. Models with a magnetic dipole offset reproduce the overall characteristics of the observed line variability, including the line equivalent width and the motion of the subpeak in the red absorption trough.     

Hα spectropolarimetry of the Herbig Ae star AB Aurigae

We present spectropolarimetric observations, obtained at H α , of the Herbig Ae star AB Aurigae. Changes in linear polarization across the H α line probe structure in the immediate circumstellar environment of the central star, down to scales of the order of one to a few stellar radii. In the case of AB Aurigae the observed polarimetric signature is complex. After applying a correction for foreground continuum polarization, we find that there is a linear-polarized H α emission component intrinsic to the source. Rotation of the angle of polarization through the emission-line profile suggests scattering in a rotating circumstellar disc. The magnetic accretor model commonly applied to T Tauri stars shows promise of explaining these data.     

The nearest star of spectral type O3: a component of the multiple system HD 150136

From radial velocities determined in high signal-to-noise digital spectra, we report the discovery that the brightest component of the binary system HD 150136 is of spectral type O3. We also present the first double-lined orbital solution for this binary. Our radial velocities confirm the previously published spectroscopic orbital period of 2.6 d. He  ii absorptions appear double at quadratures, but single lines of N  v and N  iv visible in our spectra define a radial velocity orbit of higher semi-amplitude for the primary component than do the He  ii lines. From our orbital analysis, we obtain minimum masses for the binary components of 27 and  18 M_⊙  . The neutral He absorptions apparently do not follow the orbital motion of any of the binary components, thus they most probably arise in a third star in the system.