Erratum: “Study of the optical variability of T Tau in the period 1962–2003” [Astron. Lett. 31 (2), 109 (2005)] (original) (raw)
Related papers
Study of the optical variability of T Tau in the period 1962–2003
Astronomy Letters, 2005
We present the results of our long-term U BV R observations of the star T Tauri performed at Mt. Maidanak Observatory from 1986 until 2003. These data, together with previous photoelectric observations of other authors, suggest that the long-term variations of the light curve are not periodic, but have a cycle with a time scale of 6-9 yr. The light curve also exhibits slower variations with time scales of ∼30-40 yr. We confirm the existence of periodic brightness variations with a period of P = 2 d .798 over many years; this process is peculiar in that the phase and shape of the phase curve change from season to season. We analyze the color behavior of the star. We found evidence of a strong flare occurred on October 5, 1999, when the brightness of the star reached 9 m . 22. This is the strongest flare recorded during its photoelectric observations. c 2005 Pleiades Publishing, Inc.
The Spectral Variability of the Classical T Tauri Star DR Tauri
The Astronomical Journal, 2001
We present the analysis of 103 spectra, collected over more than a decade, of the classical T Tauri star DR Tau observed with the Hamilton echelle spectrograph at Lick Observatory. The star exhibits strong emission lines that show substantial variety and variability in their proÐle shapes. The emission lines show signatures of both outÑow and infall, which vary on multiple timescales. The system shows quasiperiodic variations in line intensity and wavelength, but we are unable to recover a unique period that describes all the data. The Balmer and He I line changes are well correlated and appear to result from real variations in the accretion and wind Ñows, as opposed to apparent variations caused by changes in the veiling continuum Ñux. The Balmer line proÐles are generally strongly peaked in the red (v D 100 km s~1) and do not resemble published theoretical magnetospheric accretion proÐles. We suggest that the system is seen nearly pole-on. Coupled with a line emissivity that increases strongly near the stellar surface, this can explain the strongly asymmetric Balmer line proÐles. The Ca II and He I emission-line components are found to be very symmetric and Gaussian in shape, suggesting production in a turbulent (possibly magnetic) region. An additional sporadic high-velocity outÑow component is seen in the Balmer lines and He I. The main characteristic of the lines is their dramatic variability, which indicates a very dynamic interaction between the star and the disk. This is illustrated in several MPEGs animations showing the line proÐle variations of DR Tau, which are available on CD-ROM and the World Wide Web.6
Photometric variability of the T Tauri star TW Hya on time-scales of hours to years ★
Monthly Notices of the Royal Astronomical Society, 2008
MOST (Microvariability & Oscillations of STars) and ASAS (All Sky Automated Survey) observations have been used to characterize photometric variability of TW Hya on time scales from a fraction of a day to 7.5 weeks and from a few days to 8 years, respectively. The two data sets have very different uncertainties and temporal coverage properties and cannot be directly combined, nevertheless, they suggests a global variability spectrum with "flicker noise" properties, i.e. with amplitudes a ∝ 1/ √ f , over > 4 decades in frequency, in the range f = 0.0003 to 10 cycles per day (c/d). A 3.7 d period is clearly present in the continuous 11 day, 0.07 d time resolution, observations by MOST in 2007. Brightness extrema coincide with zero-velocity crossings in periodic (3.56 d) radial velocity variability detected in contemporaneous spectroscopic observations of Setiawan et al. (2008) and interpreted as caused by a planet. The 3.56/3.7 d periodicity was entirely absent in the second, four times longer MOST run in 2008, casting doubt on the planetary explanation. Instead, a spectrum of unstable single periods within the range of 2-9 days was observed; the tendency of the periods to progressively shorten was well traced using the wavelet analysis. The evolving periodicities and the overall flicker-noise characteristics of the TW Hya variability suggest a combination of several mechanisms, with the dominant ones probably related to the accretion processes from the disk around the star.
Results of the ROTOR-program. I. The long-term photometric variability of classical T Tauri stars
Astronomy and Astrophysics
Context. T Tauri stars exhibit variability on all timescales, whose origin is still debated. Aims. We investigate the long term variability of CTTs over up to 20 years, characterize it from a set of statistical parameters and discuss its origin. Methods. We present a unique, homogeneous database of photometric measurements for Classical T Tauri stars extending up to 20 years. The database contains more than 21 000 U BV R observations of 72 CTTs. All the data were collected within the framework of the ROTOR-program at Mount Maidanak Observatory (Uzbekistan) and together they constitute the longest homogeneous, accurate record of TTS variability ever assembled. We characterize the long term photometric variations of 49 CTTs with sufficient data to allow a robust statistical analysis and propose an empirical classification scheme. Results. Several patterns of long term photometric variability are identified. The most common pattern, exhibited by a group of 15 stars which includes T Tau itself, consists of low level variability (∆V ≤0.4mag) with no significant changes occurring from season to season over many years. A related subgroup of 22 stars exhibits a similar stable long term variability pattern, though with larger amplitudes (up to ∆V ≃1.6 mag). Besides these representative groups, we identify three smaller groups of 3-5 stars each which have distinctive photometric properties. Conclusions. The long term variability of most CTTs is fairly stable and merely reflects shorter term variability due to cold and hot surface spots. Only a small fraction of CTTs undergo significant brightness changes on the long term (months, years), which probably arise from slowly varying circumstellar extinction. Key words. stars: activity of stars -pre-main-sequence stars -variables: general 2 K.N. Grankin et al.: Results of the ROTOR-program. I. The long-term photometric variability of CTTs
Results of the ROTOR-program-II. The long-term photometric variability of weak-line T Tauri stars
Context. T Tauri stars exhibit variability on all timescales, whose origin is still debated. On WTTS the variability is fairly simple and attributed to long-lived, ubiquitous cool spots. Aims. We investigate the long term variability of WTTS, extending up to 20 years in some cases, characterize it statistically and discuss its implications for our understanding of these stars. Methods. We have obtained a unique, homogeneous database of photometric measurements for WTTS extending up to 20 years. It contains more than 9 000 UBV R observations of 48 WTTS. All the data were collected at Mount Maidanak Observatory (Uzbekistan) and they constitute the longest homogeneous record of accurate WTTS photometry ever assembled. Results. Definitive rotation periods for 35 of the 48 stars are obtained. Phased light curves over 5 to 20 seasons are now available for analysis. Light curve shapes, amplitudes and colour variations are obtained for this sample and various behaviors exhibited, discussed and interpreted. Conclusions. Our main conclusion is that most WTTS have very stable long term variability with relatively small changes of amplitude or mean light level. The long term variability seen reflects modulation in the cold spot distributions. Photometric periods are stable over many years, and the phase of minimum light can be stable as well for several years. On the long term, spot properties do change in subtle ways, leading to secular variations in the shape and amplitudes of the light curves.
TIME VARIABILITY OF EMISSION LINES FOR FOUR ACTIVE T TAURI STARS. I. OCTOBER–DECEMBER IN 2010
The Astronomical Journal, 2013
We present optical spectrophotometric monitoring of four active T Tauri stars (DG Tau, RY Tau, XZ Tau, RW Aur A) at high spectral resolution (R 1 × 10 4 ), to investigate the correlation between time variable mass ejection seen in the jet/wind structure of the driving source and time variable mass accretion probed by optical emission lines. This may allow us to constrain the understanding of the jet/wind launching mechanism, the location of the launching region, and the physical link with magnetospheric mass accretion. In 2010, observations were made at six different epochs to investigate how daily and monthly variability might affect such a study. We perform comparisons between the line profiles we observed and those in the literature over a period of decades and confirm the presence of time variability separate from the daily and monthly variability during our observations. This is so far consistent with the idea that these line profiles have a long term variability (3-20 years) related to episodic mass ejection suggested by the structures in the extended flow components. We also investigate the correlations between equivalent widths and between luminosities for different lines. We find that these correlations are consistent with the present paradigm of steady magnetospheric mass accretion and emission line regions that are close to the star.
The Astrophysical Journal, 2002
We present the analysis of 42 spectra of the Classical T Tauri star TW Hya observed with the FEROS echelle spectrograph over 2 yr. We determined the rotational and radial velocities of TW Hya, obtaining v sin i ¼ 5 AE 2 km s À1 and v rad ¼ 12:5 AE 0:5 km s À1 . The star exhibits strong emission lines that show substantial variety and variability in their profile shapes. Emission lines such as H, H, and He i show both outflow and infall signatures, which change on different timescales. The system displays periodic variations in line and veiling intensities, but the stellar rotation period remains uncertain. We see evidence of a variation in the mass accretion rate over a 1 yr period from the Na D line profiles that are well fitted by magnetospheric accretion models with moderate mass accretion rates (10 À9 up to 10 À8 M yr À1 ). The lower values inferred from the models are close to the average mass accretion rate obtained from the veiling estimates (~2 Â 10 À9 M yr À1 ), but the veiling results are consistent with a constant mass accretion rate within the errors of the calculations. The H, He i, Na D, and H emission-line equivalent widths corrected from veiling correlate well with each other and are correlated with the veiling, indicating the same mechanism should be powering them and suggesting an origin related to the accretion process. The wings of the main emission lines are generally correlated, except when the Balmer lines exhibit properties suggesting a strong contribution from a wind. The blueward absorption components of the Balmer lines, most likely from a wind, are not correlated with veiling. The spectroscopic analysis allows us to infer the inclination of the stellar rotation axis (i ¼ 18 AE 10 ) that matches the current estimations of the disk orientation (0 < i < 15 ). A magnetospheric dipole axis that is misaligned with the stellar/disk rotation axis could produce the observed photometric variability, and we tend to favor a low inclination but not a totally face-on geometry for the system. TW Hya exhibits typical spectral characteristics of many classical T Tauri stars in Taurus despite its older age, indicating that active accretion disks can readily survive up to 10 Myr.
On the nature of variations in the T Tauri star WY Arietis (LkHα264)
Astronomy & Astrophysics, 2002
We report optical spectroscopic and photometric results from our long-term study of the T Tauri star WY Arietis (LkHα 264). The data gathered show different types of variability: variations in the continuum level, in the emission line fluxes and line profiles. The timescales associated with these variations appear quite diverse. The correlation found between the variations observed in the veiling and in the continuum flux strongly suggest that an extra continuum source veiling the stellar photospheric spectrum is the cause driving the continuum variability. The present work also unveils the presence of an accretion flow onto the star, as revealed by the O I λ7773Å and λ8446Å line profiles, which is the first unambiguous model-independent detection of such an event in this star. Our photometric data allowed us to find a period of 3.04 days for this star, somewhat in tune with Fernandez & Eiroa (1996). However, due to the poor time sampling our finding should be taken as tentative. A detailed analysis of the broad and narrow components of the He I line profiles indicates the presence of a hot wind during the November 1993 observation while in October 1999 a wind is only revealed by the blue wing asymmetry of the observed Balmer and CaII infrared triplet line profiles. The correlation between the strength of the hot wind and the amount of flux in the emission lines led also to the conclusion that this type of wind provides a significant contribution to the hydrogen and metal emission lines. We have also witnessed an exceptional activity during one of the nights which may be attributed to an increase in LkHα 264's accretion rate or to a flare-like event. Although it is not possible to clearly distinguish between these possibilities, the available data set points towards variable accretion as being responsible for the observed event.
Photometry and spectroscopy of RV Tauri stars
2020
RV Tauri stars are recognized as radially pulsating, post-Asymptotic Giant Branch stars, in the high-luminosity end of type-II Cepheids. They show characteristic light modulations and spectral line variations which are generally linked with intrinsic radial pulsations and resulting shock waves. This thesis investigates stellar pulsations in a sample of RV Tauri stars using a mix of analytical methods. In particular, it examines the short-term and long-term variability by searching for periodicities in the photometric and spectroscopic data for a number of selected southern hemisphere RV Tauri stars. These data are used to explore how the variability and other observed stellar properties, fit within the current theories which explain RV Tauri behaviour as being due to stellar pulsation, binarity, and interaction with its local environment, including circumbinary dust. We use extensive visual photometric data from the AAVSO International Database for analysing the long-term and short-term variations and recent BV data for analysing the short-term pulsations. AAVSO's VPhot was used to perform differential photometry for the BV data and Period04 was used for Fourier analysis and least-squares fitting in a pre-whitening manner to find periodicites in both visual and BV data. Both short-term pulsational and most of the long-term periods of all the stars studied were found to be in reasonable agreement with the published values. The amplitude of the long-term periods was substantial in variation. Complex peak structures are seen in periodograms possibly owing to period changes over time and/or "flips" seen in the deep-shallow light curve alternation with time. These variations in both short and long-term periods (and also amplitude) over time is confirmed in wavelet analysis of U Mon and IW Car. Nearly 100 spectra of U Mon were acquired over 5 months to cover ∼1.5 cycles of its 92-day pulsation period. Effects of two pulsation-related shock-waves per pulsation cycle were seen on specific spectral line profiles, consistent with previous studies. The new pulsational radial velocity curves measured by Gaussian profile fitting to the Fe I line at 6200.313Å show well-defined consistency with the published pulsational radial velocity curve. The results in this thesis add depth and scope to the leading RV Tauri model which explains the light and spectral variations in RVb stars through a combination of binarity, intrinsic stellar pulsations, interaction and obscuration mechanisms involving binaries and circumstellar/circumbinary disk depending on the observer's perspective.