COYOTES IV: the rotational periods of low-mass Post-T Tauri stars in Taurus (original) (raw)
Related papers
The X-ray activity-rotation relation of T Tauri stars in Taurus-Auriga
Astronomy & Astrophysics, 2007
Context. The Taurus-Auriga star-forming complex hosts the only population of T Tauri stars in which an anticorrelation of X-ray activity and rotation period has been observed. Aims. We aim to explain the origin of the X-ray activity-rotation relation in Taurus-Auriga. We also aim to put the X-ray activity of these stars into the context of the activity of late-type main-sequence stars and T Tauri stars in the Orion Nebula Cluster. Methods. We have used XMM-Newton's European Photon Imaging Cameras to perform the most sensitive survey to date of X-ray emission (0.3-10 keV) from young stars in Taurus-Auriga. We investigated the dependences of X-ray activity measures-X-ray luminosity, L X , its ratio with the stellar luminosity, L X /L , and the surface-averaged X-ray flux, F XS-on rotation period and compared them with predictions based solely on the observed dependence of L X on a star's L and whether it is accreting or not. We tested for differences in the distributions of L X /L of fast and slow rotators, accretors and non-accretors, and compared the dependence of L X /L on the ratio of the rotation period and the convective turnover timescale, the Rossby number, with that of late-type main-sequence stars. Results. We found significant anticorrelations of L X and F XS with rotation period, but these could be explained by the typically higher stellar luminosity and effective temperature of fast-rotators in Taurus-Auriga and a near-linear dependence of L X on L. We found no evidence for a dependence of L X /L on rotation period, but for accretors to have lower L X /L than non-accretors at all rotation periods. The Rossby numbers of accretors and non-accretors were found to be the same as those of late-type main-sequence stars showing saturated X-ray emission. Conclusions. Non-accreting T Tauri stars show X-ray activity entirely consistent with the saturated activity of fast-rotating late-type main-sequence stars. Accreting T Tauri stars show lower X-ray activity, but this cannot be attributed to their slower rotation.
Rotation effects in classical T Tauri stars
Astronomy Letters, 2012
Surface temperature inhomogeneities in classical T Tauri stars (CTTS) induced by magnetic activity and mass accretion lead to rotational modulation of both photometric and spectroscopic parameters of these stars. Using the extended photometric catalogue by Grankin et al. , we have derived the periods and amplitudes of the rotational modulation of brightness and color for 31 CTTS; for six of them, the periods have been revealed for the first time. The inclinations of the rotation axis and equatorial rotational velocities of CTTS have been determined. We show that the known periods of brightness variations for some of the CTTS are not the axial rotation periods but are the Keplerian periods near the inner boundary of the dusty disk. We have found that the angular velocity of CTTS with a mass of 0.3-3 M ⊙ in the Taurus-Auriga complex remains constant in the age range 1-10 Myr. CTTS on radiative evolutionary tracks rotate faster than completely convective CTTS. The specific angular momentum of CTTS depends on the absolute luminosity in the Hα line.
Rotation periods of Post-T Tauri stars in Lindroos systems
Astronomy and Astrophysics, 2004
We present a rotational study of Post-T Tauri stars (PTTSs) in Lindroos systems, defined as binaries with early type primaries on the main-sequence (MS) and late-type secondaries on the pre-main-sequence (PMS) phase. The importance of this study in comparison with previous ones is that the Lindroos sample is not X-ray selected so we avoid a possible bias towards fast rotators. In this preliminary study we have monitored eleven stars in the UBVRI bands during two campaigns of ten consecutive nights each. Eight of the observed PTTSs show periodic modulations in their lightcurves and the derived periods range from 1.9 d to 8.0 d. The comparison of these results with theoretical rotational tracks based on disk-star locking theory shows that star-disk decoupling times of 1−20 Myr could reproduce the rotational properties of the targets, assuming an initial rotation period of ∼8 d and a mass of 1 M. We have studied the rotation-activity relations of Lindroos PTTSs and compared them with those found in other groups of PMS and zero-age main-sequence (ZAMS) ∼1 M stars. The Lindroos sample displays activity-rotation relations very similar to those found in TTSs. It contains a mixture of very active stars, with L X /L bol ratios close to the saturation level of-3, and less active (unsaturated) stars. This could be the result of different star-disk decoupling times. Future monitoring of a larger and unbiased sample of PTTS will be important to confirm the significance of these results.
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.
Rotationally modulated X-ray emission from T Tauri stars
Monthly Notices of the Royal Astronomical Society, 2006
We have modelled the rotational modulation of X-ray emission from T Tauri stars assuming that they have isothermal, magnetically confined coronae. By extrapolating surface magnetograms we find that T Tauri coronae are compact and clumpy, such that rotational modulation arises from X-ray emitting regions being eclipsed as the star rotates. Emitting regions are close to the stellar surface and inhomogeneously distributed about the star. However some regions of the stellar surface, which contain wind bearing open field lines, are dark in X-rays. From simulated X-ray light curves, obtained using stellar parameters from the Chandra Orion Ultradeep Project, we calculate X-ray periods and make comparisons with optically determined rotation periods. We find that X-ray periods are typically equal to, or are half of, the optical periods. Further, we find that X-ray periods are dependent upon the stellar inclination, but that the ratio of X-ray to optical period is independent of stellar mass and radius.
The Astrophysical Journal Supplement Series, 2012
We analyze light curves obtained by the Trans-atlantic Exoplanet Survey (TrES) for a field centered on the L1495 dark cloud in Taurus. The Spitzer Taurus Legacy Survey catalog identifies 179 bona fide Taurus members within the TrES field; 48 of the known Taurus members are detected by TrES, as well as 26 candidate members identified by the Spitzer Legacy team. We quantify the variability of each star in our sample using the ratio of the standard deviation of the original light curve (σ orig. ) to the standard deviation of a light curve that has been smoothed by 9 or 1001 epochs (σ 9 and σ 1001 , respectively). Known Taurus members typically demonstrate (σ orig. /σ 9 ) < 2.0, and (σ orig. /σ 1001 ) < 5, while field stars reveal (σ orig. /σ 9 ) ∼ 3.0 and (σ orig. /σ 1001 ) ∼ 10, as expected for light curves dominated by unstructured white noise. Of the 74 Taurus members/candidates with TrES light curves, we detect significant variability in 49 sources. Adapting a quantitative metric originally developed to assess the reliability of transit detections, we measure the amount of red and white noise in each light curve and identify 18 known or candidate Taurus members with highly significant period measurements. These appear to be the first periods measured for four of these sources (HD 282276, CX Tau, FP Tau, TrES J042423+265008), and in two other cases, the first non-aliased periods (LkCa 21 and DK Tau AB). For the remainder, the TrES measurements typically agree very well (δP < 1%) with previously reported values. Including periods measured at lower confidence for 15 additional sources, we report periods for 11 objects where no previous periods were found, including 8 confirmed Taurus members. We also identify 10 of the 26 candidate Taurus members that demonstrate variability levels consistent with being bona fide T Tauri stars. A Kolomgorov-Smirnov (K-S) test confirms that these new periods confirm the distinction between the rotation period distributions of stars with and without circumstellar disks, with only a 10% probability of the two populations sharing the same parent period distribution. K-S tests do suggest, however, that the updated Taurus period distribution now more closely resembles those measured in other young star-forming clusters (i.e., NGC 2264, NGC 6530, and the ONC). This improved agreement may reflect the exclusion of long rotation periods which are detected in Taurus at lower significance, and which may be beyond the limits of detectability in more distant star-forming regions.
Identification of Isolated Post T Tauri Stars in the Solar Neighborhood
Astrophysics and Space Science Proceedings, 2010
Post T Tauri stars (PTTS) are late-type stars in the age range between 10 and 100 Myr filling the gap between T Tauri (TTS) and zero-age main sequence phases. This period of evolution remains ambiguous and until now different studies of young stars have failed to find the numbers of PTTS that are expected. In the last years, some PTTS have been identified among the X-ray detected pre-main sequence stars in some star-forming regions. More recently, additional PTTS have been identified in young associations and moving groups (β Pic, TW Hya, Tucana/Horologium, and the AB Dor). However, many isolated PTTS still remain undiscovered. In this contribution, we compiled the PTTS previously identified in the literature, and identified new candidates using the information provided by the high resolution spectra obtained during our surveys of late-type stars possible members to young moving groups, FGK stars in the solar neighborhood. To identify PTTS we applied an ageoriented definition using relative age indicators (Li abundance, chromospheric and coronal emission and the kinematics) as well as color-magnitude diagrams and premain sequence isochrones.
2009
Post T Tauri stars (PTTS) are late-type stars in the age range between 10 and 100 Myr filling the gap between T Tauri (TTS) and zero-age main sequence phases. This period of evolution remains ambiguous and until now different studies of young stars have failed to find the numbers of PTTS that are expected. In the last years, some PTTS have been identified among the X-ray detected pre-main sequence stars in some star-forming regions. More recently, additional PTTS have been identified in young associations and moving groups (β Pic, TW Hya, Tucana/Horologium, and the AB Dor). However, many isolated PTTS still remain undiscovered. In this contribution, we compiled the PTTS previously identified in the literature, and identified new candidates using the information provided by the high resolution spectra obtained during our surveys of late-type stars possible members to young moving groups, FGK stars in the solar neighborhood, and RasTyc sample. To identify PTTS we applied an age-oriented definition using relative age indicators (Li abundance, chromospheric and coronal emission and the kinematics) as well as color-magnitude diagrams and pre-main sequence isochrones.
Mid-Infrared Observations of T Tauri Stars: Probing the Star-Disk Connection in Rotational Evolution
Astronomical Journal, 2006
We present mid-IR N-band (λ ef f = 10.2µm) photometry of a carefully selected sample of T Tauri stars thought to be single from the Taurus-Auriga molecular cloud. Infrared excesses in these stars are generally attributed to circumstellar dust-disks. Combining observations at 2.16µm (K s -band) and 10.2µm (N-band) we probe a region in the circumstellar dust-disk from a few stellar radii through the terrestrial planet zone (0.02-1.0AU). By analyzing the distribution of the (K s − N) color index with respect to previously measured photometric rotation periods we investigate what role circumstellar disks play in the rotational evolution of the central star. The resulting positive correlation between these two variables is consistent with the notion that a star-disk interaction facilitates the regulation of angular momentum during the T Tauri stage. We also demonstrate, how including non-single stars in such an analysis will weaken any correlation in the relation between (K s − N) color and period. To further understand disk properties we also present SEDs for a few objects with new ground based Mband (λ ef f = 4.8µm) and Q-band (λ ef f = 20µm) data and compare them to a geometrically thin, optically-thick disk model.
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.