RR Tau Research Articles

Modelling UX Ori star eclipses based on spectral observations with the Nordic Optical Telescope − I. RR Tau

ABSTRACT Based on observations obtained with the Nordic Optical Telescope (NOT) we investigate the spectral variability of the Herbig Ae star RR Tau. This star belongs to the UX Ori family, characterized by very deep fadings caused by the screening of the star with opaque fragments (clouds) of the protoplanetary discs. At the moments of such minima one observes strong spectral variability due to the fact that the dust cloud occults, for an observer, not only the star but also a part of the region where the emission spectrum originates. We calculated a series of obscuration models to interpret the observed variability of the H α line parameters. We consider two main obscuration scenarios: (1) the dust screen rises vertically above the circumstellar disc, and (2) the screen intersects the line-of-sight moving azimuthally with the disc. In both cases, the model of the emission region consists of a compact magnetosphere and a magnetocentrifugal disc wind. Comparison with observations shows that the first scenario explains well the variability of the radiation flux, the equivalent width, as well as the asymmetry of the H α line during eclipses, while the second scenario explains them only partly. This permits us to suggest that in the case of RR Tau, the main causes of the eclipses are either a structured disc wind, or the charged dust lifted along the field lines of the poloidal component of the magnetic field of the circumstellar disc.

Photometric activity of UX orionis stars and related objects in the near infrared and optical: CO Ori, RR Tau, UX Ori, and VV Ser

This paper continues a study of the photometric activity of UX Ori stars in the optical and near-infrared (JHKLM bands) initiated in 2000. For comparison, the list of program stars contains two Herbig Ae stars that are photometrically quiet in the optical: MWC480 andHD179218. Fadings ofUXOri stars in the optical (V band) due to sporadic increases of the circumstellar extinction are also observed in the infrared (IR), but with decreasing amplitude. Two stars, RR Tau and UX Ori, displayed photometric events when V -band fadings were accompanied by an increase in IR fluxes. Among the two Herbig Ae stars that are photometrically quiet in the optical, MWC 480 proved to be fairly active in the IR. Unlike the UX Ori stars, the variation amplitude of MWC 480 increases from the J band to the M band. In the course of the observations, no deep fadings in the IR bands were detected. This indicates that eclipses of the program stars have a local nature, and are due to extinction variations in the innermost regions of the circumstellar disks. The results presented testify to an important role of the alignment of the circumstellar disks relative to the direction towards the observer in determining the observed IR variability of young stars.

Cardioprotection by 6-gingerol in diabetic rats

The current study was conducted to evaluate the effect of 6-gingerol (6G) on cardiac complications in streptozotocin (STZ)-induced diabetic (DM) rats. STZ-induced DM rats (single 50 mg/kg i.p. injection, 15 days prior to drug treatment) or time-matched controls were treated with 6G (75 mg/day route orally). After a further 8 weeks, blood was collected for biochemical analysis and 8-isoprostenol was measured in urine. Cardiac hemodynamics and ECG was assessed. 6G significantly attenuated the increased level of blood glucose in diabetic rats and improved cardiac hemodynamics in including RR interval, max dP/dt, min dP/dt and Tau. In addition, 6G alleviated the elevated ST segment, T amplitude and R amplitude with no significant effect on disturbed levels of adiponectin, TGF-β or 8-isoprostenol induced by diabetes. The results showed that treatment with 6G has an ameliorative effect on cardiac dysfunction induced by diabetes. Which may be not related to its potential antioxidant effect.

MONITORING HαEMISSION AND CONTINUUM OF UXORs: RR Tauri

The Maria Mitchell Observatory, in collaboration with the Astrokolkhoz Observatory, started a program of photometric monitoring of UX Ori-type stars (UXORs) with narrowband interference filters (IFs; augmented with the traditional broadband filters) aimed at separating the Hα emission variations from those of the continuum. We present the method of separation and the first results for RR Tau obtained in two seasons, each roughly 100 days long (2010 Winter-Spring and 2010 Fall-2011 Spring). We confirm the conclusion from previous studies that the Hα emission in this star is less variable than the continuum. Although some correlation between the two is not excluded, the amplitude of Hα variations is much smaller (factors of 3-5) than that of the continuum. These results are compatible with Grinin's model of UXORs, which postulates the presence of small obscuring circumstellar clouds as the cause of the continuum fading, as well as the presence of a circumstellar reflection/emission nebula, larger than the star and the obscuring clouds, which is responsible for Hα emission and the effect of the color reversal in deep minima. However, the results of both our broadband and narrowband photometry indicate that the obscuration model may be insufficient to explain all of the observations. Disk accretion, the presence of stellar or (proto) planetary companion(s), as well as the intrinsic variations of the star, may contribute to the observed light variations. We argue, in particular, that the Hα emission may be more closely correlated with the intrinsic variations of the star than with the much stronger observed variations caused by the cloud obscuration. If this hypothesis is correct, the close monitoring of Hα emission with IFs, accessible to small-size telescopes, may become an important tool in studying the physical nature of the UXORs' central stars.

Parameters of Herbig Ae/Be and Vega-type stars

Context. This work presents the characterization of 27 young early-type stars, most of them in the age range 1‐10 Myr, and three ‐suspected‐ hot companions of post-T Tauri stars belonging to the Lindroos binary sample. Most of these objects show IR excesses in their spectral energy distributions, which are indicati ve of the presence of disks. The work is relevant in the fields o f stellar physics, physics of disks and formation of planetary systems. Aims. The aim of the work is the determination of the effective temperature, gravity, metallicity, mass, luminosi ty and age of these stars. An accurate modelling of their disks needs, as a previ ous step, the knowledge of most of these parameters, since they will determine the energy input received by the disk and hence, its geometry and global properties. Methods. Spectral energy distributions and mid-resolution spectra were used to estimate Teff, the effective temperature. The comparison of the profiles of the Balmer lines with synthetic pro files provides the value of the stellar gravity, g∗. High-resolution optical observations and synthetic spectra are used to estimate the metallicity, [M/H]. Once Teff, g∗ and [M/H] are known for each star, evolutionary tracks and isochrones provide estimations of the mass, luminosity, age and distances (or upper limits in some cases). The method is original in the sense that it is distance-indep endent, i.e. the estimation of the stellar parameters does n ot require, as it happens in other works, the knowledge of the distance to the object. Results. Stellar parameters (effective temperature, gravity, metallicity, mass, luminosi ty, age and distances ‐or upper limits) are obtained for the sample of stars mentioned above. A detailed discussion on some individual objects, in particular VV Ser, RR Tau, 49 Cet and the three suspected hot companions of post-T Tauris, is presented. Conclusions. These results, apart from their intrinsic interest, would b e extremely valuable to proceed a step further and attempt to model the disks surrounding the stars. The paper also shows the diffi culty posed by the morphology and behaviour of the system star+disk in the computation of the stellar parameters.

The Herbig Ae/Be Star V586 Ori

Studies of the Herbig Ae/Be star V586 Ori based on photoelectric observations in the Stromgren system are reported. It is found that as the brightness decreases, the Balmer discontinuity index initially increases and then begins to drop. As the star fades, the index β decreases. We have previously found similar variations in the indices β and C for UX Ori, RR Tau, and V351 Ori. It is shown that V586 Ori has the characteristics of a shell-star.

Observations of a unique minimum of RR Tau in the optical and near infrared

We present observations of the UX Ori star RR Tau in the optical (UBVRI)and near infrared (JHKLM)acquired between November 2000 and April 2001. We recorded a uniquely long (about half a year) Algol-like minimum with an amplitude of ΔV≈2.9. The dimming of RR Tau was accompanied by an increase of the linear polarization, typical of UX Ori stars and testifying to the eclipsing nature of the minimum. The J and H infrared fluxes varied synchronously with the optical variations. However, the K and L brightness changes were in the opposite sense: the flux in these two bands increased for the entire duration of the optical minimum. Our analysis suggests that the source of the K and L radiation is the dust cloud itself, moving at a distance of about 1 AU from the star. The flux increase in these bands was not due to an increase in the dust temperature, but instead to an increase in the number of emitting grains in the cloud. This could be associated either with an actual increase in the number of fine grains due to sublimation and the disruption of larger grains or with the distortion and disruption of the cloud due to tidal perturbation, permitting the star’s light to penetrate and heat the densest regions of the cloud. Based on the observed L fluxes, we estimate the mass of the emitting dust in the cloud to be ≈1023 g. Taking into account the presence of cool dust and a gaseous component in the cloud in addition to the dust heated by the star’s radiation, and adopting a ratio for the masses of the dust and gas components similar to that in the interstellar medium (1:100), we estimate the cloud’s total mass to be ≥1025 g. Judging from this value and the duration of the minimum, we observed an extremely rare episode associated with a giant gas and dust cloud with a total mass on the order of 0.1 lunar mass or higher, which passed very near the young star (and may be falling onto it).

Optical spectra of five UX Orionis-type stars

We present in this paper several high resolution () spectra of five UXORs (UX Ori, CQ Tau, BF Ori, RR Tau, WW Vul), which cover the entire visual range, from 3900 to about 8700 Å. There are between 4 and 7 spectra per star, obtained over a time interval of two years. Simultaneous or quasi-simultaneous photometric observations were also obtained at the Crimean Astrophysical Observatory. The complete, reduced and normalized spectra are available in electronic form. We show for each star a selection of the most interesting lines, and the full spectrum of UX Ori computed by averaging the spectra obtained when the star was at maximum light. For UX Ori we show also the synthetic spectrum and provide an identification of most of the lines. The spectra are too sparse to form true time sequences; however, they provide an extremely useful database for studies of UX Ori-type stars. We discuss briefly the main features of the spectra. We show that they contain many time-stable photospheric lines that can be described to a good approximation by the synthetic spectra of normal A stars with and we derive for each star effective temperature, gravity and rotational velocity. We examine the time variability of selected lines and study their connection with the photometric activity of the stars. Two different types of spectral variability are identified. One is common to all stars with circumstellar (CS) gas and is caused by perturbations of the physical and kinematic conditions of the emitting region. There is no correlation between this type of activity and the brightness variations of the star. On the contrary, a second type of spectral variability correlates well with the brightness variations and is very likely connected with the screening effect of an opaque dust cloud which sporadically intersects the line of sight. This type of variability has been observed in its simplest form in one of the RR Tau spectra, where the equivalent width of the forbidden line [Oi] 6364 Å increased by a factor of about three as the star faded by approximately the same amount.

The Hα, Hβ, AND Hδ lines in the spectrum of RR Tauri

The results of spectroscopic study of Ae Herbig star RR Tau are reported. The observations were carried out with a moderate resolution. In accordance with the presented data the Halpha line exhibits a double-peaked emission profile. The blue component is weaker than or equal to the red one. Variations of the Halpha equivalent width by a factor of 4 - 5 were found. The structure of this line also varies. On JD 2447148 a red absorption reversal of the Halpha profile was observed. The Hbeta spectral line exhibited both emission and absorption. On JD 2449664 the single-peak emission shifted to the short wavelength range of the underlying absorption line and the red wing of the stellar line looked like a red-shifted absorption component of medium strength. The Hdelta line was in absorption.

Photometric investigation and rapid periodicity of RR Tau

Results are given for photoelectric UBV, photographic B, and infrared RJHK observations of the variable Be star RR Tau, which is 8 arcmin from the transient x-ray source A0535 + 26. The total amplitude of the variability of the star in the period 1967 to 1978 reaches 4 mag. The changes in the color indices are appreciable (0.3 to 0.6 mag), but are not correlated with the brightness, although, on the average, the star is somewhat bluer at maximum light. Photometry in the U filter with a time resolution of 10 sec revealed the presence of a rapid (of the order of one minute) variability of the star with amplitude of about 10%. The rapid variability contains a periodic component with amplitude 2% and P 47 sec, which is close to one of the harmonics (46 sec) of the x-ray pulsar.