We analyzed the frequency domain of time series of simulated ZZ Ceti light-curves to investigate the detectability and period recovery performance of short period variables (periods < 2 hours) for the Gaia mission. In our analysis, first we used a non-linear ZZ Ceti light-curves simulator code to simulate the variability of ZZ Ceti stars (we assumed stationary power spectra over five years). Second we used the Gaia nominal scanning law and the expected photometric precision of Gaia to simulate ZZ Ceti time series with Gaia's time sampling and photometric errors. Then we performed a Fourier analysis of these simulated time series. We found that a correct period can be recovered in ~65% of the cases if we consider Gaia per CCD time series of a G ~ 18 magnitude multiperiodic ZZ Ceti star with 5%-10% light-curve variation. In the pre-whitened power spectrum a second correct period was also recovered in ~26% of the cases.
Deep Dive into Detecting short period variable stars with Gaia.
We analyzed the frequency domain of time series of simulated ZZ Ceti light-curves to investigate the detectability and period recovery performance of short period variables (periods < 2 hours) for the Gaia mission. In our analysis, first we used a non-linear ZZ Ceti light-curves simulator code to simulate the variability of ZZ Ceti stars (we assumed stationary power spectra over five years). Second we used the Gaia nominal scanning law and the expected photometric precision of Gaia to simulate ZZ Ceti time series with Gaia’s time sampling and photometric errors. Then we performed a Fourier analysis of these simulated time series. We found that a correct period can be recovered in ~65% of the cases if we consider Gaia per CCD time series of a G ~ 18 magnitude multiperiodic ZZ Ceti star with 5%-10% light-curve variation. In the pre-whitened power spectrum a second correct period was also recovered in ~26% of the cases.
Detecting short period variable stars with Gaia
Mihaly Varadi1, Laurent Eyer1, Stefan Jordan2, Nami Mowlavi1, Detlev Koester3
1 – Geneva Observatory, University of Geneva, ch. des Maillettes 51, CH-1290 Sauverny, Switzerland
2 – ARI/ZAH, Univ. of Heidelberg, Mönchhofstr. 12-14, D-69120 Heidelberg, Germany
3 – Institut für Theoretische Physik und Astrophysik, University of Kiel, Leibnizstraße 15, D-24098 Kiel, Germany
Abstract. We analyzed the frequency domain of time series of simulated ZZ Ceti light-curves to investigate the
detectability and period recovery performance of short period variables (periods < 2 hours) for the Gaia mission. In our
analysis, first we used a non-linear ZZ Ceti light-curves simulator code to simulate the variability of ZZ Ceti stars (we
assumed stationary power spectra over five years). Second we used the Gaia nominal scanning law and the expected
photometric precision of Gaia to simulate ZZ Ceti time series with Gaia’s time sampling and photometric errors. Then
we performed a Fourier analysis of these simulated time series. We found that a correct period can be recovered in ~65%
of the cases if we consider Gaia per CCD time series of a G ~ 18 magnitude multiperiodic ZZ Ceti star with 5%-10%
light-curve variation. In the pre-whitened power spectrum a second correct period was also recovered in ~26% of the
cases.
Keywords: Gaia mission - short period variables - variability - detections - simulations - ZZ Ceti stars.
PACS: 97.30.Dg, 95.75.Wx, S 95.40.+s
INTRODUCTION
The ESA Gaia satellite will observe about one
billion stars with unprecedented astrometric and
photometric precision. Over its 5 year mission, it will
systematically scan all the sky and observe sources
from 40 to 250 times, down to magnitude G ~ 20 mag.
See info-sheet at http://www.rssd.esa.int/Gaia for a
more detailed description of the satellite.
TABLE 1. Types and properties of short period variables.
Type
Periods
[minutes]
Amplitudes
[mag]
β Cep stars
96 - 480
< 0.1
δ Scuti stars
28 - 480
0.003 - 0.9
roAp stars
6 - 21
< 0.01
EC14026 stars
1.3 - 8.3
< 0.03
Betsy stars (PG1716)
33 - 150
< ~0.01
ZZ Ceti stars (DAV)
0.5 - 25
0.001 - 0.3
V777 Her stars (DBV)
2 - 16
0.001 - 0.2
GW Vir stars (DOV +
PNNVs)
5 - 85
0.001 - 0.2
Eclipsing white dwarfs
> 6
< 0.7
The Gaia time sampling and the CCD data
acquisition scheme allow in principle to probe stellar
variability on time scales even as short as several tens
of seconds, thereby giving potential access to the study
of variable stars in a large and homogenous sample of
stars. A first study was done by Eyer & Mignard
(2005) on the correct detection rate of monoperiodic
signals for a wide range of periods. They concluded
that periods of regular variable star can be recovered
even from signals with low S/N ratio and that the
period recovery depends mainly on the ecliptic
latitude. Later Mary et al. (2006) presented a work on
the detectability of low amplitude short period
multiperiodic signals, which correspond to pulsation
modes of roAp stars. Our goal is to extend these
studies using more realistic light-curve models for
several types of variables stars (see Table 1), which
are showing variability on timescales less than 2 hours.
We call these short period variables. The variability
amplitudes of short period variables are mostly at
millimagnitude level, so that a good photometric
precision is a key point to the detection of such kind of
stars. Gaia’s design seems to meet this requirement
(see Fig. 1 for the expected photometric precision of
Gaia).
In this article we are analyzing simulated Gaia time
series of ZZ Ceti variables. ZZ Ceti stars are
multiperiodic white dwarf pulsators (DAVs), which
are oscillating in low order non-radial gravity modes
(see e.g. Montgomery in these proceedings). From the
point of view of our analysis, it is worth to note, that
most of the ZZ Ceti stars show amplitude, period and
mode changes on timescales from weeks to years,
which causes that their power spectra are not
stationary over the mission life time of Gaia. The
study of such light-curves is not part of this work, but
we plan to investigate the detectability of variables
which do not have stationary power spectra.
FIGURE 1. Expected photometric precisions of Gaia:
per-CCD, per transit, and over the whole mission. In
the last two cases the dependence on spectral types is
also shown. Only the photon noise is taken into
account, but calibration uncertainties will dominate the
bright end. Figure by C.Jordi (private communication)
modified by M.Varadi.
LIGHT-CURVE SIMULATIONS
To perform tests on the detectability of ZZ Ceti
stars from Gaia like photometry, first we simulate
continuous ZZ Ceti light-curves, second we generate
Gaia time series from these by taking into account the
time sampling and photometric precision of the Gaia
satellite.
ZZ Ceti light-curves simulation
We use a non
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