Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPhotometric/spectroscopic analyses and magnetic activity in young late-type stars
516
0
0.0
(
0
)
Authors
K. Biazzo
Ask ChatGPT about the research
No Arabic abstract
We present the work in progress of a study based on photometric and spectroscopic observations of young Weak-line T Tauri and Post T Tauri stars just attiving on the Zero Age Main Sequence. This study is part of a project based on high-resolution spectra obtained with FOCES@CAHA (Spain) and SARG@TNG (Spain) and contemporaneous photometry performed at Catania (Italy) and Ege (Turkey) observatories. The main aim is to investigate the topology of magnetic active regions at photospheric and chromospheric levels in young single stars. Since our targets are slow rotators (vsini < 25 km/s), corresponding to rotation periods larger than about 2 days, we are able to apply the spectroscopic technique based on line-depth ratio for the measure of the photospheric temperature modulation. These stars, possible members of Stellar Kinematic Groups, display emission cores in the CaII H&K and IRT lines, as well as a conspicuous filling-in of the Halpha core. Moreover, we detect absorption of the HeI-D3 line, coming from the upper chromospheric layers, derive the lithium abundance (age indicator), and measure the rotational and radial velocities. We find a clear rotational modulation, due to photospheric spots, both in the light and the temperature curves. The Halpha and the CaII-IRT emissions display a fair variation correlated with the rotation. Finally, we are developing a spot/plage model to reproduce the data and derive the spot parameters (namely, filling factor and temperature) and to recover information about the chromospheric inhomogeneities (flux contrast and filling factor). This study is very important to explore the correlations between global stellar parameters (e.g., surface gravity, effective temperature) and spot/plage characteristics in stars with different activity level and evolutionary stage.
rate research
Read More
We study a sample of 21 young and active solar-type stars with spectral types ranging from late F to mid K and characterize the behaviour of their activity. We apply the continuous period search (CPS) time series analysis method on 16 to 27 years of photometry to estimate the surface differential rotation and determine the existence and behaviour of active longitudes and activity cycles on the stars. We supplement the time series results by calculating new $log{R_{rm HK}}$ emission indices for the stars from high resolution spectroscopy. The photometric rotation period variations reveal a positive correlation between the relative differential rotation coefficient and the rotation period, but do not reveal any dependence of the differential rotation on the effective temperature of the stars. Secondary period searches reveal activity cycles in 18 of the stars and temporary or persistent active longitudes in 11 of them. The activity cycles fall into specific activity branches. We find a new split into sub-branches, indicating multiple simultaneously present cycle modes. Active longitudes appear to be present only on the more active stars. There is a sharp break at approximately $log{R_{rm HK}}=-4.46$ separating the less active stars with long-term axisymmetric spot distributions from the more active ones with non-axisymmetric configurations. In seven out of eleven of our stars with clearly detected long-term non-axisymmetric spot activity the estimated active longitude periods are significantly shorter than the mean photometric rotation periods. This systematic trend can be interpreted either as a sign of the active longitudes being sustained from a deeper level in the stellar interior than the individual spots or as azimuthal dynamo waves exhibiting prograde propagation.
Aims: We present a compilation of spectroscopic data from a survey of 144 chromospherically active young stars in the solar neighborhood which may be used to investigate different aspects of the formation and evolution of the solar neighborhood in terms of kinematics and stellar formation history. The data have already been used by us in several studies. With this paper, we make all these data accessible to the scientific community for future studies on different topics. Methods: We performed spectroscopic observations with echelle spectrographs to cover the entirety of the optical spectral range simultaneously. Standard data reduction was performed with the IRAF ECHELLE package. We applied the spectral subtraction technique to reveal chromospheric emission in the stars of the sample. The equivalent width of chromospheric emission lines was measured in the subtracted spectra and then converted to fluxes using equivalent width-flux relationships. Radial and rotational velocities were determined by the cross-correlation technique. Kinematics, equivalent widths of the lithium line 6707.8 angstroms and spectral types were also determined. Results: A catalog of spectroscopic data is compiled: radial and rotational velocities, space motion, equivalent widths of optical chromospheric activity indicators from Ca II H & K to the calcium infrared triplet and the lithium line in 6708 angstroms. Fluxes in the chromospheric emission lines and RHK are also determined for each observation of star in the sample. We used these data to investigate the emission levels of our stars. The study of the Halpha emission line revealed the presence of two different populations of chromospheric emitters in the sample, clearly separated in the log F(Halpha)/Fbol - (V-J) diagram.
Here, BV(RI)c broad band photometry and intermediate resolution spectroscopy in Halpha region are presented for two rapidly rotating late-type stars: EY Dra and V374 Peg. For a third rapid rotator, GSC 02038-00293, intermediate resolution Halpha spectroscopy and low resolution spectroscopy are used for spectral classification and stellar parameter investigation of this poorly known object. The low resolution spectrum of GSC 02038-00293 clearly indicates that it is a K-type star. Its intermediate resolution spectrum can be best fitted with a model with Teff=4750K and vsini=90km/s, indicating a very rapidly rotating mid-K star. The Halpha line strength is variable, indicating changing chromospheric emission on GSC 02038-00293. In the case of EY Dra and V374 Peg, the stellar activity in the photosphere is investigated from the photometric observations, and in the chromosphere from the Halpha line. The enhanced chromospheric emission in EY Dra correlates well with the location of the photospheric active regions, indicating that these features are spatially collocated. Hints of this behaviour are also seen in V374 Peg, but it cannot be confirmed from the current data. The photospheric activity patterns in EY Dra are stable during one observing run lasting several nights, whereas in V374 Peg large night-to-night variations are seen. Two large flares, one in the Halpha observations and one from the broadband photometry, and twelve smaller ones were detected in V374 Peg during the observations spanning nine nights. The energy of the photometrically detected largest flare is estimated to be 4.25x10^31 - 4.3x10^32 ergs, depending on the waveband. Comparing the activity patterns in these two stars, which are just below and above the mass limit of full convection, is crucial for understanding dynamo operation in stars with different internal structures.
We investigate photometric variations due to stellar activity which induce systematic radial-velocity errors (so-called jitter) for the four targets in the Hyades open cluster observed by the K2 mission (EPIC 210721261, EPIC 210923016, EPIC 247122957, and EPIC 247783757). Applying Gaussian process regressions to the K2 light curves and the near-infrared (NIR) light curves observed with the IRSF 1.4-m telescope, we derive the wavelength dependences of the photometric signals due to stellar activity. To estimate the temporal variations in the photometric variability amplitudes between the two observation periods of K2 and IRSF, separated by more than 2 years, we analyze a number of K2 targets in Hyades that have also been observed in Campaigns 4 and 13 and find a representative variation rate over 2 years of 38%pm71%. Taking this temporal variation into account, we constrain projected sizes and temperature contrast properties of the starspots in the stellar photosphere to be approximately 10% and 0.95, respectively. These starspot properties can induce relatively large differences in the variability amplitude over different observational passbands, and we find that radial-velocity jitter may be more suppressed in the NIR than previously expected. Our result supports profits of on-going exoplanet search projects that are attempting to detect or confirm young planets in open clusters via radial-velocity measurements in the NIR.
We present new 14 high-resolution echelle spectra to discuss the level of chromospheric activity of DM UMa in {He I} D3, {Na I} D1, D2, Halpha, and {Ca II} infrared triplet lines (IRT). It is the first time to discover the emissions above the continuum in the {He I} D3 lines on 2015 February 9 and 10. The emission on February 9 is the strongest one ever detected for DM UMa. We analysed these chromospheric active indicators by employing the spectral subtraction technique. The subtracted spectra reveal weak emissions in the {Na I} D1, D2 lines, strong emission in the Halpha line, and clear excess emissions in the {Ca II} IRT lines. Our values for the EW8542/EW8498 ratio are on the low side, in the range of 1.0-1.7. There are also clear phase variations of the level of chromospheric activity in equivalent width (EW) light curves in these chromospheric active lines (especially the Halpha line). These phenomena might be explained by flare events or rotational modulations of the level of chromospheric activity.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
