1
HIGH TEMPORAL RESOLUTION SPECTROSCOPY
OF LATE-TYPE RAPID ROTATOR STARS:
BD +20º1790
Hernán-Obispo M., De Castro E., Cornide M.,
Crespo-Chacón I., Gálvez M.C., López-Santiago J.
Departamento de Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain.
Observations
BD +20º 1790
Abstract
In this contribution we present the results of high temporal
resolution spectroscopic observations of the K5Ve star
BD+20º1790.
BD +20º 1790 was clasificated by Jeffries et. Al (1995) as a
KVe star with V=9.9. Montes et al. (2001) proposed its
membership in the Local Association moving group.
High resolution echelle spectra have been obtained in February
2004 using SOFIN spectrograph at 2.56m Nordic Optical
Telescope (NOT, La Palma) and in Abril 2004 using FOCES
spectrograph in 2.2m Telescope at Calar Alto Observatory.
We have detected strong chromospherical activity in this
star in a previous observing run ( 2.2m-FOCES 2002/04 ). In
this run a strong flare was observed. In spite of the fact
that BD+20º1790 rotational velocity is approximately 10
km/s , the emission in chromospheric lines Hαα and Hββ is
very strong and lead us to make a detailed study of the
existence of chromospheric structures like plages or
prominences.
In each run continuous series of spectra were taken during
visibility time of the star. The analysis of these spectra allow
us to monitoring the temporal evolution of line profile to
several chromospherical activity indicators, like Hα . From the
EW and the CCF bisector variation with time, it is possible to
detect the presence of prominence-like clouds (dense and cool
material embedded in the hotter stellar corona). In addition,
the simultaneous analysis of different optical chromospheric
indicators (Hβ (4861 Å) and HeI D3 (5876 Å)) lead us to
discriminate what kind of structure we are detecting in Hα
line.
We present the of the study of chromospheric and
photospheric activity.
Transient absorption features
15
We study the Hα line variation to infer the kind of
structure present in the chromosphere. The
chromospheric contribution has been determined
using the spectral subtraction technique.
Fig.1 shows the profile line variation. On the left is
the sequence of subtracted spectra of Hα line. The
ratio spectra were obtained using the average of all
the observations.They are show on the right of the
Fig. 1. Averaging all the spectra it is expected to
remove effects due to transient events in the
profile. The shape of the average profile will not be
affected significantly.
19
10
Figure
Figure 33 .. Bisector
Bisector of
of the
the subtracted
subtracted
spectra
spectra of
of Hα
Hα line
line for
for the
the 02/02/2004.
02/02/2004.
Figure
Figure 1.
1. The
The number
number is
is related
related to
to
the
the observation
observation number
number in
in the
the night
night
10
4
1
Figure 2 . Time sequence occur 1 to 15
The dynamic ratio spectrum was constructed by
dividing each individual subtracted spectrum by
an average of all observations and then displacing
consecutive vertically with one spectrum per line.
Time runs from bottom to top. The features
marked with red arrows in Fig. 1 are seen clearly
in the dynamic ratio spectrum. In nº 4 and
nº 15,they appear more brillant, they are in
emission. In nº 1 and nº 10, they appear more
darked, they are in absorption in Fig. 1.
Chromospheric activity indicators
The wavelength range covers with 2.2m FOCES
configuration allow us to study the behaviour of
different optical chromospheric activity indicators,
from the Ca II H and K to the Ca II IRT lines.
Spectra of the quiescent state of BD +20º1790 in
the Ca II H and K, Hδ, Hγ, Hβ, Hα, He I D3 and Ca
II IRT lines are presented in the figures. For each
region we have plotted the observed spectrum (solidline) and the synthetic spectrum(dashed-line) in the
left, and the subtracted spectra in the right.
Strong emission is observed in Ca II H and K, Ca II
IRT, Hα and all the Balmer serie lines.
b) 29 March to 7 April 2004 using FOCES spectrograph in 2.2 m
Telescope at Calar Alto Observatory . The FOCES spectrograph
was usd with a 2048x2048 pixel 150µ Site#1d15 CCD detector.
With this configuration the wavelength range covers from 3720 Å
to 10850 Å in 100 orders, including CaII IRT (8498,8542,8662 Å)
and Hα (6562.8 Å). The reciprocal dispersion achieved ranges
from 0.04 to 0.13 Å /pixel, and the resolution 0.08 to 0.35 Ǻ
(FWHM)
In order to obtain high temporal resolution a continuous
series of spectra were taken, with exposure time of 600 sec
and S/N ≈50.
BD+20º1790 has not been well studied. The rotational and
photometric periods are an uncertainly, the photometry is
imcomplete and there isn’t a preliminary spectroscopic
study to tipify the chromospheric and photospheric
activity.
Profile line variation
15
The spectroscopic observations of BD+20º1790 were obtained
during two observing runs:
a) 2, 5, 6, 7 February 2004 using SOFIN spectrograph at 2.56m
Nordic Optical Telescope (NOT, La Palma). The SOFIN spectrograph
was used with the camera 1 and the 2052x2052 Piskonov Loral
CCD as detector. With this configuration the wavelength range
covers from 4200 Å to 7490 Å in 24 orders, including Hβ (4861 Å)
,HeI D3 (5876 Å) and Hα (6562.8 Å). The reciprocal dispersion
achieved ranges from 0.019 to 0.03 Å /pixel, and the resolution
0.07 to 0.16 Ǻ (FWHM)
Figure
Figure 44 .. Profiles
Profiles of
of Hα
Hα line
line for
for the
the
transient.
transient. Time
Time occur
occur 10
10 to
to 19
19
Prominence-like clouds can be detected as transient
absorption features moving across the Hα line profile.
To study profile variations we have used the bisectors
technique, calculating a bisector for line profile.
Temporal evolution of bisectors show in Fig. 3, for the
first night of NOT-SOFIN run.
Any feature moving across the Hα profile must
disturb the bisector. Variations in the asymmetry
are related with the presence of transient of
prominences. A completed transient was detected in
this night. It is marked in Fig. 3 with a dashed
elipse. The time of the transient was about 2h,
smoller than rotational period, and in agreement with
typical transient times. It is indicated that the
feature we are detecting it not a superficial
feature.
Photospheric activity
Flare event
In the FOCES 04A run a flare event was observed at night 7 April.Fig.5
and Fig.6 show the sequence of consecutive line profiles of Hα,Hβ and He
I D3 and gradual decay of the flare.
The flare maximum is marked with bold line. Minimum Hα and Hβ width is
marked with black spotted line and maximum width is marked with green
spotted line.
The wings of the Hα and Hβ profile are more wider the flare maximum.
The HeI D3 emission (marked with a red line) is strongest when the flare
is at maximum and shows a progresive decrease during the gradual decay.
Fig.7 and Fig.8 show the dynamic spectrum for the observations of Hα and
Hβ line profile. Every observation has a time of integration of 10 minutes.
We only observed the gradual decay of the flare, during ~ 2h 40m.
The first observation may be near the flare maximum.
Fig.5 and Fig. 6
Sequence of
consecutive Hα and
He I D3 line
profile (left) and
Hβ and He I D3
line profile (right)
Heliocentric radial velocities were determined using
the cross-correlation technique. The spectra of the
star was correlated order by order, against spectra
of several radial velocity standars. Orders with
chromospheric features and telluric lines were
excluded. The radial velocities calculated for each
order were weighted by their errors. Every point in
the figure represents an observation of these star in
the 2.2m FOCES run.
Differences up to 1 km/s are measured in the
values. These variations are larger than the
individual measurement error ( ~ 0.10 km/s).
The presence of star
spots can disturb the
profile of photospheric
lines and induce
variations in the
measured radial velocity.
Probably,we are
detecting spot activity
in the photosphere of
BD +20º1790
Fig. 9. Radial velocities for 2.2m FOCES run
Fig.7 and Fig. 8.
Dynamic spectrum
for Hα line (left)
and Hβ line (right)
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