J/A+A/588/A54 roAp star alpha Cir blue and red light curves (Weiss+, 2016)
The roAp star alpha Circinus as seen by BRITE-Constellation.
Weiss W.W., H.-E. Frohlich, Pigulski A., Popowicz A., Huber D., Kuschnig R.,
Moffat A.F.J., Matthews J.M., Saio H., Schwarzenberg-Czerny A., Grant C.C.,
Koudelka O., Luftinger T., Rucinski S.M., Wade G.A., Alves J., Guedel M.,
Handler G., Mochnacki St., Orleanski P., Pablo B., Pamyatnykh A.,
Ramiaramanantsoa T., Rowe J., Whittaker G., Zawistowski T., Zoclonska E.,
Zwintz K.
<Astron. Astrophys. 588, A54 (2016)>
=2016A&A...588A..54W 2016A&A...588A..54W (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Photometry
Keywords: stars: chemical peculiar - asteroseismology - stars: oscillation -
stars: rotation - stars individual: alpha Cir - starspots
Abstract:
We report on an analysis of high-precision, multi-colour photometric
observations of the rapidly-oscillating Ap (roAp) star alpha Cir.
These observations were obtained with the BRITE-Constellation, which
is a coordinated mission of five nanosatellites that collects
continuous millimagnitude-precision photometry of dozens of bright
stars for up to 180-days at a time in two colours (∼Johnson B and R).
BRITE stands for BRight Target Explorer. The object Cir is the
brightest roAp star and an ideal target for such investigations,
facilitating the determination of oscillation frequencies with high
resolution. This star is bright enough for complementary
interferometry and time-resolved spectroscopy. Four BRITE satellites
observed alpha Cir for 146d or 33 rotational cycles. Phasing the
photometry according to the 4.4790d rotational period reveals
qualitatively different light variations in the two photometric bands.
The phased red-band photometry is in good agreement with
previously-published WIRE data, showing a light curve symmetric about
phase 0.5 with a strong contribution from the first harmonic. The
phased blue-band data, in contrast, show an essentially sinusoidal
variation. We model both light curves with Bayesian Photometric
Imaging, which suggests the presence of two large-scale, photo-
metrically bright (relative to the surrounding photosphere) spots. We
also examine the high-frequency pulsation spectrum as encoded in the
BRITE photometry. Our analysis establishes the stability of the main
pulsation frequency over the last ∼20-years, confirms the presence of
frequency f7, which was not detected (or the mode not excited) prior
to 2006, and excludes quadrupolar modes for the main pulsation
frequency.
Description:
Te data cover 25 March - 8 August 2014: 146 days, corresponding to
nearly 33 stellar rotational cycles.
alpha Cir was observed in the blue by BAb for 131 days and BLb for 26
days; in the red by UBr for 145 days, and BTr for six days. The light
curves consist of nearly 44000 blue exposures and 69000 red exposures,
each of duration 1s in both colours.
Objects:
-------------------------------------------------
RA (2000) DE Designation(s)
-------------------------------------------------
14 42 30.42 -64 58 30.5 alpha Cir = * alf Cir
-------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
alpcirb.dat 77 37772 Processed BRITE-Constellation light curve in
BLUE filter (central wavelength ∼420nm)
alpcirr.dat 77 64191 Processed BRITE-Constellation light curve in
RED filter (central wavelength ∼620nm)
--------------------------------------------------------------------------------
See also:
J/MNRAS/386/2039 : Elemental abundances of α Cir (Bruntt+, 2008)
Byte-by-byte Description of file: alpcirb.dat alpcirr.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
3- 12 F10.6 d HJD Heliocentric Julian date (HJD-2456000)
17- 25 F9.6 mag mag Magnitude
30- 37 F8.6 mag e_mag rms uncertainty on mag
41- 45 F5.2 pix Xcen Instrument X position of center
49- 53 F5.2 pix Ycen Instrument Y position of center
57- 61 F5.2 --- T Instrument temperature (in Celcius degrees)
65- 72 F8.6 --- Diff Difference between autocorrelation and averaged
correlation with image shifted by 1 pixel in
each of four sides
75- 77 A3 --- Sat Name of the satellite (1)
--------------------------------------------------------------------------------
Note (1): Satellite names as follows:
BAb = d BRITE-Austria blue filter
BLb = BRITE-Lem blue filter
BTr = BRITE-Toronto red filter
UBr = UniBRITE red filter
--------------------------------------------------------------------------------
Acknowledgements:
Werner Weiss, werner.weiss(at)univie.ac.at
(End) Patricia Vannier [CDS] 24-Feb-2016