3 research outputs found
Photometric and spectroscopic observations of three rapidly rotating late-type stars: EY Dra, V374 Peg and GSC 02038-00293
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.Comment: Accepted for publication in Astronomische Nachrichten (Astronomical
Notes
Photometric observations from theoretical flip-flop models
Some active stars show a so-called flip-flop phenomenon in which the main
spot activity periodically switches between two active longitudes that are 180
degrees apart. In this paper we study the flip-flop phenomenon by converting
results from dynamo calculations into long-term synthetic photometric
observations, which are then compared to the real stellar observations. We show
that similar activity patterns as obtained from flip-flop dynamo calculations,
can also be seen in the observations. The long-term light-curve behaviour seen
in the synthesised data can be used for finding new stars exhibiting the
flip-flop phenomenon.Comment: 5 pages, 5 figures, accepted for publication in A&