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TNO Time Allocation Committee
Application for observing time
Cycle 2 – November 2014 through April 2015
Important Notice:
By submitting this proposal, the PI takes full responsibility for the content of the proposal. The application must be submitted via
email to [email protected] by the deadline as given in the Call for Observing Proposal (CfP).
General Information
Title
Prominences in white dwarf main sequence binaries
Abstract
Prominences are arcs of gas, held above the surface of the Sun by strong magnetic field. These atmospheric
features are also observed in other stars, such as in close binaries. In white dwarf binaries, evidence of slingshot
prominences has been recorded spectroscopically, but the limited time resolution, compared to their rapid
evolution makes them hard to study in detail. We have found what we believe to be the photometric signature of
prominences in a white dwarf / M dwarf binary star through persistent dips in flux caused by obscuration of the
white dwarf. These dips are remarkable for the high column density required to affect continuum light and for
being very long-lasting (years), while also showing signs of evolution. Here we propose to do an extensive, multiband photometric monitoring of SDSS J1021+1744 to study the evolution of prominences in this binary using the
high-speed ULTRASPEC camera. Time on parallel spectroscopy monitoring is going to be requested at the ESO
VLT.
Number of nights or hours (specify n or h)
Dark
Grey
Bright
Any
i) request for this period
66hrs
0
0
0
ii) minimum useful allocation for this period
50hrs
0
0
0
iii) already awarded to this project
Total
-
iv) still required to complete this project
Total
-
Is this a Guaranteed Time Observation (GTO) application: No
Preferred month(s): December-April
Visitor or Service Mode: Visitor
Target name
RA (hh:mm)
DEC (dd:mm)
Mag. Limit
Instrument*
SDSS J1021+1744
10:21:02.254
+17:44:39.96
g ~19
ULTRASPEC
Targets observability for the proposed date(s): Yes
Principal Investigator
Affiliation
Email
Contact number
Puji Irawati
NARIT
[email protected]
053-225569
Co-investigators
Affiliation
Observer
Student
Tom Marsh, Madelon Bours,
Elme Breedt, Boris Gaensicke
Univ. of Warwick
Yes
No
No, Yes
No, No
Nuanwan Sanguansak
Suranaree Univ.
Maybe
No
Steven Parsons
Univ. del Valparaiso
No
No
Takashi Hattori
NAOJ-Subaru
No
No
Vik Dhillon, Stuart Littlefair
Liam Hardy
Univ. of Sheffield
Yes
No
Yes
Is this proposal linked to a Master/PhD thesis preparation? State name(s) and role(s) of the student(s)
No
Description of the proposed project
A) Scientific Rationale:
Prominences and flares are two of many atmospheric activities exhibited by our Sun. In these events, large
amounts of material are released from the Sun’s surface, often thousand of kilometres up from the Sun’s
photosphere. Prominences are arcs of gas, held above the surface of the Sun by a strong magnetic field. This gas,
which contains cool and dense material, will appear as dark filamentz against the Solar disk. Typical prominences
erupt quickly and last several minutes to hours, but the quiescent ones can persist for weeks or months.
Prominences are also observed in other stars such as in the young T Tauri stars, where the eruptions are thousand
times more energetic and frequent than the ones of our Sun (Aarnio et al. 2012). In close binaries, evidences of
slingshot prominences have been recorded spectroscopically by several authors, e.g. QS Vir (Parsons et al. 2011),
SDSS J0039+0054 (Southworth et al. 2010), AM Her (Gaensicke et al.1998), IP Peg and SS Cyg (Steeghs et al.
1996). The eruptive events in these binaries are known to originate from the active M dwarf companions.
The first photometric signature of prominence comes from the observation of QS Vir by O’Donoghue et al. 2003
(Figure 1, left). From the light curve of QS Vir, it seems that the prominences in QS Vir can reach such highcolumn densities that they completely obscure the white dwarf in continuum light. The continuum dips of QS Vir
were seen just once in 37 eclipses by O’Donoghue et al, and in no other observations since, despite significant
further coverage (e.g. Parsons et al 2010).
During our runs with the 2.4m Thai National Telescope in January 2014, we observed a similar photometric
signature on SDSS J1021+1744, another eclipsing post common-envelope binaries which, however, is much
fainter than QS Vir. The first report of an unusual drop of brightness in this binary comes from Parsons et al.
(2011) where the authors suggest that this change in brightness is caused by flare from the M dwarf star. Our
follow-up observations of this star revealed multiple post-eclipse dips that occur ~15min after the egress of the
white dwarf (Figure 1, right). These dips, which seems to be consistent in phase, appear to be a long-lasting
feature, although they do show evolution in shape and intensity. The sharp and deep profiles of the dips suggest
that the material obscuring the white dwarf is dense but small in size (or located quite far from the white dwarf).
We also obtained the full-orbit light curve of SDSS J1021+1744 in r’ filter (Figure 2) to try to detect the signature
of the prominences as they pass in front of the M dwarf. The light curve exhibits a large flare before the primary
eclipse, which confirms that the M dwarf companion is an active star. Apart from this flaring event, we are not
able to detect the presence of the companion star. Further observations in the red are needed to give affirmation to
this finding.
The observation of SDSS J1021+1744 from the Thai National Observatory is part of a campaign to monitor the
evolution of the dips in this system. We will combine the data obtained with TNT+ULTRASPEC with the results
from other telescopes to probe the detailed structure and evolution of stellar prominences. We aim to do so using
the observations by our team from these facilities: VLT+XSHOOTER (optical-NIR spectroscopy, Parsons et al.);
WHT+ULTRACAM (u’-g’-i’ bands photometry, Marsh et al.); Subaru+FOCAS (u-band photometry,
Hattori/Richichi et al.)
Figure 1. Left: The (only) appearance of pre-eclipse dips in QS Vir system observed by O’Donoghue et al (2003).
The white dwarf is completely obscured by the dense materials ejected from the prominences. Right: Light curve
of J1021+1744 observed from TNO in g’ filter. The dips in this systems has a complex shape and occur after the
white dwarf eclipse.
Figure 2. Full orbital light curve in r’-filter covering two successive primary eclipses in J1021+1744. The structure
of the dips have changed since our observation in January (Fig.1). One large flare takes place around phase 0.75
before the second white dwarf eclipse, consistent with the M dwarf being a very active star. The light curve shows
orbital modulation due to the shape of the companion star, but we are unable to detect the secondary eclipse.
References:
Aarnio, A. et al, 2012, MNRAS,421,1797
Gaensicke, B. et al., 1998, A&A, 338, 933
Parsons, S. et al, 2010, MNRAS, 407, 2362
Parsons, S. et al, 2011, MNRAS, 412, 2563
O’Donoghue, D. et al, 2003, MNRAS, 345, 506
Southworth, J. et al, 2010, A&A, 524, 86
Steeghs, D. et al, 1996, MNRAS, 281, 626
B) Observational Requirements:
Our choice falls on ULTRASPEC because this camera has ideal sensitibility and time resolution to our target (u’mag>20.0). We will observe in g’, r’, i’, and KG5 filters. This will allow us to be sensitive to prominences passing
in front of both the white dwarf (in g and KG5) and the M dwarf (in r’ and i’). Unfortunately SDSS J1021+1744
is too faint to be observed using u’ filter at TNT, although it is very desirable to obtain some at shorter
wavelengths. The 8’x8’ field of view of ULTRASPEC will allow us to monitor our target and several comparison
stars simultaneously. We will use full frame with 2x2 binning or smaller window with normal binning to achieve
<10s sampling time. Depending on the sky conditions, we expect to reach as fast as 4sec sampling during a good
night.
The ULTRASPEC imaging ETC (courtesy of V. Dhillon) reports SNR~15 with 4s integration time (19.5mag
star, g-filter, 2x2) using normal readout mode. Altough the SNR value is quite low with our choice of integration
time, we prefer to execute our observations in fast exposure to be able to see the shape of the dips in detail. The
data frames can be binned/combined offline to obtain a better SNR for further analysis.
C) Previous allocation:
Previous observations of SDSS J1021+1744 at TNO were part of the proposal “White Dwarf Binaries: Follow-up
on three eclipsing WDMS binaries” with N. Sanguansak as the PI. The proposal was awarded three nights of
observations using ULTRASPEC. Our target star was also observed several times during the GTO, carried out by
our UK collaborators, as well as during other observing slots allocated to programs with P. Irawati as PI. We
obtained a good number of light curves in different filters, where some of them cover full orbital phase. The data
from these observations have been analysed and publication is in preparation. However, we experienced a
problem with the ULTRASPEC filter positioning that has provided some difficulties. We hope this issue will be
fixed in Cycle 2.
3
Justification of requested observing time and lunar phase:
Lunar phase is crucial because our target is very faint (g’=19.51) and we need a good SNR with integration time
<10s. Dark nights are highly preferable, although grey nights are also acceptable if the Moon sets early in the
night. The orbital period of our target is ~3.3hrs, and we will focus around phase 0.8-1.3 (±110min) to cover the
primary eclipse and the dips. Our goal is to get 15-20 times of the light curves around the orbital phase mentioned
above over five months period, therefore 50hours is our minimum request and shared nights are acceptable.
In few occasions, we will monitor this star continuously for ~5-6hrs (for two consecutive eclipses+dips) to see the
short term variability of the dips.
Strategy for data reduction and analysis:
We will use the provided ULTRASPEC pipeline and data reduction software for our data analysis. The data
obtained from TNO will be combined with the result from other telescopes (e.g. photometric data from Subaru
and WHT, VLT spectroscopic data). Our team is composed of experts in the reduction and analysis of
ULTRASPEC photometric data.
Time constraints:
In November our target is not yet observable, while during the first half of December and second part of April our
source is visible with airmass>2 for less than 4 hours.
Applicant’s publications related to the subject of this proposal during the last 3 years (maximum 10 papers):
Bours, M. et al, 2014, MNRAS, 438, 3399, Precise parameters for both white dwarfs in the eclipsing binary CSS
4117
Parsons, S. et al, 2014, MNRAS, 438, L91,Timing variations in the secondary eclipse of NN Ser
Marsh, T. et al, 2014, MNRAS, 437, 475, The planets around NN Serpentis: still there
Richichi, A. et al. 2014, First Lunar Occultation Results from the 2.4m Thai National Telescope equipped with
ULTRASPEC, Astronomical Journal in press (http://arxiv.org/abs/1408.0073)
Littlefair,S. et al. 2014, MNRAS, submitted, The substellar companion in the eclipsing white dwarf binary SDSS
J141126.20+200911.1
Irawati P. et al., 2013, Population synthesis of cataclysmic variable star: I. A new methodology and initial study
on the post common-envelope stage, ApSS, 346, 79
Instrumentation*
Imaging: Yes
Instrument(s): ULTRASPEC
Filter(s): g’r’i’KG5
Spectroscopy: No
Instrument(s):
Visitor Instrument: Please specify. It is highly recommended that contacts are taken with OPD well in advance.
For TAC and OPD use only
Application No.:
Allocated night(s):
Assigned astronomical technician:
Special remarks:
(Puji Irawati)
Principal Investigator
*
Please check see the CfP for the list of currently available instruments and their general specifications.