ترغب بنشر مسار تعليمي؟ اضغط هنا

Activity trends in young solar-type stars

278   0   0.0 ( 0 )
 نشر من قبل Jyri Lehtinen
 تاريخ النشر 2015
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

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.



قيم البحث

اقرأ أيضاً

Stellar winds govern the spin-down of Solar-type stars as they age, and play an important role in determining planetary habitability, as powerful winds can lead to atmospheric erosion. We calculate three-dimensional stellar wind models for five young Solar-type stars in the Hyades cluster, using TOUPIES survey stellar magnetograms and state-of-the-art Alfven wave driven wind modelling. The stars have the same 0.6-Gyr age and similar fundamental parameters, and we account for the uncertainty in and underestimation of absolute field strength inherent in Zeeman-Doppler imaging by adopting both unscaled and scaled (by a factor of five) field strengths. For the unscaled fields, the resulting stellar wind mass loss is 2-4 times greater and the angular momentum loss 2-10 times greater than for the Sun today, with the scaled results correspondingly greater. We compare our results with a range published of wind models and for the Alfven wave driven modelling see evidence of mass loss saturation at about $10 dot M_odot$.
The surface rotation rates of young solar-type stars decrease rapidly with age from the end of the pre-main sequence though the early main sequence. This suggests that there is also an important change in the dynamos operating in these stars, which s hould be observable in their surface magnetic fields. Here we present early results in a study aimed at observing the evolution of these magnetic fields through this critical time period. We are observing stars in open clusters and stellar associations to provide precise ages, and using Zeeman Doppler Imaging to characterize the complex magnetic fields. Presented here are results for six stars, three in the in the beta Pic association (~10 Myr old) and three in the AB Dor association (~100 Myr old).
Surface rotation rates of young solar-type stars display drastic changes at the end of the pre-main sequence through the early main sequence. This may trigger corresponding changes in the magnetic dynamos operating in these stars, which ought to be o bservable in their surface magnetic fields. We present here the first results of an observational effort aimed at characterizing the evolution of stellar magnetic fields through this critical phase. We observed stars from open clusters and associations, which range from 20 to 600 Myr, and used Zeeman Doppler Imaging to characterize their complex magnetic fields. We find a clear trend towards weaker magnetic fields for older ages, as well as a tight correlation between magnetic field strength and Rossby number over this age range. Comparing to results for younger T Tauri stars, we observe a very significant change in magnetic strength and geometry, as the radiative core develops during the late pre-main sequence.
127 - A. Frasca 2010
We present the results of contemporaneous spectroscopic and photometric monitoring of the young solar-type star HD171488 (Prot~1.337 d) aimed at studying surface inhomogeneities at photospheric/chromospheric levels. Echelle FOCES spectra (R~40000) an d Johnson photometry have been performed in 2006. Spectral type, rotational velocity, metallicity, and gravity were determined using a code developed by us. The metallicity was measured from the analysis of iron lines. The spectral subtraction technique was applied to the most relevant chromospheric diagnostics included in the FOCES spectral range (CaII IRT, Halpha, HeI-D3, Hbeta, CaII H&K). A model with two large high-latitude spots is sufficient to reproduce the B/V light curves and the radial velocity modulation, if a temperature difference between photosphere and spots of 1500 K is used. A Doppler imaging analysis of photospheric lines confirms a similar spot distribution. With the help of an analogous geometric two-spot model, we are able to reproduce the modulations in the residual chromospheric emissions adopting different values of ratios between the flux of plages and quiet chromosphere (5 for Halpha and 3 for CaII). Facular regions of solar type appear to be the main responsible for the modulations of chromospheric diagnostics. Both the spot/plage model and the cross-correlation between the light curve and the chromospheric line fluxes display a lead effect of plages with respect to spots (20-40 deg in longitude). The active regions of the rapidly rotating star HD171488 are similar to the solar ones in some respect, because the spot temperature is close to that of sunspot umbrae and the plage flux-contrast is consistent with the average solar values. The main differences with respect to the Sun are larger sizes and higher latitudes.
The properties of the acoustic modes are sensitive to magnetic activity. The unprecedented long-term Kepler photometry, thus, allows stellar magnetic cycles to be studied through asteroseismology. We search for signatures of magnetic cycles in the se ismic data of Kepler solar-type stars. We find evidence for periodic variations in the acoustic properties of about half of the 87 analysed stars. In these proceedings, we highlight the results obtained for two such stars, namely KIC 8006161 and KIC 5184732.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا