N.N. Samus1,2,3
S.V. Antipin2,1
1Institute of Astronomy, Russian Acad. Sci.
2Sternberg Astronomical Institute, Moscow University
3Euro-Asian Astronomical Society
Variable Stars
and Data-Intensive Astronomy
XXVIII General Assembly of the IAU, SPS15
Beijing, August 31, 2012
Principal problem: No amplitude limit defining a variable star.
General Catalogue of Variable Stars: peak-to-peak amplitudes from
>19m (V1500 Cyg) down to 0.004m (α Aql).
The combined light curve of
V1500 Cyg (Nova Cyg 1975)
18 hours of space-borne infrared
photometry of Altair (D. Buzasi et
al., 2005, ApJ, 619, 1072)
Beijing, 2012
CCD Discoveries of Galactic Variable Stars
USNO-B1.0 catalog (2003):
1,042,618,261 objects (stars and galaxies),
~ 1 billion stars to 20–21m
One star of 80–100 is variable at the 0m.03–0m.05 level,
and thus ~10 million variable stars are potentially detectible with a
ground-based 1-m telescope, ordinary CCD detector, and standard
software for automatic search for variable stars.
Currently (August 2012) known are ~ 212000 variable stars of our
Galaxy (International Star Register of the AASVO – VSX, the web
facility working quite independently of the GCVS but keeping close
everyday contact), i.e. ~2% of those potentially detectable using
CCD techniques.
Beijing, 2012
Prospects of Variable-Star Discoveries
known variables
200 000
Variables not yet known
10 000 000
And what is this?
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V376 Peg (HD 209458): the
first star of our Galaxy with
photometrically detected
transits of a big exoplanet
across the stellar disk (S. Jha
et al., 2000, 540, L45). New
possibilities for surface
mapping! Such eclipses are
observable even for amateur
astronomers.
Beijing, 2012
A transit observed for the same star by the Hubble Space Telescope
(T. Brown et al., 2001, ApJ, 552, 699)
Beijing, 2012
The ASAS-3 survey (G. Pojmanski). Two 20-cm telescopes. Southern
sky. Some 30000 new variable stars. Observations of some 15000000
stars online.
Beijing, 2012
The ROTSE-I/NSVS survey. Northern sky. A small fraction of
possible variable-star discoveries made by the authors, photometry of
about 14000000 stars online. The light curve shown is for T And
Beijing, 2012
By New Year 2012, open access was provided
to photometry of the Catalina Sky Survey (50 –
70-cm Schmidt telescopes, all the northern sky
except the Milky Way strip, very-high-quality
photometry, working magnitudes from 13 to 19)
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New Types
Accretion-Disk Precession
(A.V. Khruslov, 2011, PZP, 11, 17)
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RR Lyrae Stars with Two Closely Spaced
Frequencies
P1/P2 = 0.90 ÷ 0.99
(S. Antipin & J. Jurcsik, 2005, IBVS,
No. 5632)
Beijing, 2012
Considerable Number Increase of Several
Variability Types During Recent Years
• BY Dra / RS CVn
• High-Amplitude Delta Scuti Stars (HADSs)
• Double-Mode Cepheids
• Eclipsing Variables
Beijing, 2012
Number increase of known double-mode Cepheids (mainly due to
data mining in ASAS-3 data)
18 in 2000
38 in 2010
(23 of them, F+1O,
and 15, 1O+2O)
Khruslov’s discoveries
(as of 2012):
12 double-mode
Cepheids,
11 of them 1O+2O
+ 3 similar RR near
galactic plane
(A.V. Khruslov, 2010, PZP, 10, 16)
Beijing, 2012
One of the scanners used to digitize the Moscow plate stacks
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D.M. Kolesnikova et al. (2008, AcA, 58,
279; 2010, ARep, 54, 1000) discovered,
in a field of 100 square degrees
reasonably well studied using traditional
methods, almost 500 new variable stars.
Beijing, 2012
Number Increase of Known HADS Variables
(D.M. Kolesnikova et al., 2010)
Search for variables using scans of plates from Moscow stacks. In the
field centered at 66 Oph, 10°x10° (less than 0.25% of the total area of
the sky), 13 HADSs were detected, leading to an estimate >5000 for
the whole sky. The GCVS number of Delta Scuti stars with
amplitudes of at least 0m.2 is 121.
Beijing, 2012
Different Period Distribution of Eclipsing Stars
from the Same Scans
The period distribution of newly discovered eclipsing stars is
considerably shifted towards shorter periods (the GCVS frequencies
are in brackets):
P
0.2–0.4 d
0.4–0.6 d
0.6–0.8 d
0.8–1.0 d
>1 d
EA
EB
13% (1.7%)
47% (15.4%)
22% (3.7%) 22% (17.8%)
17% (5.0%) 9% (13.4%)
61% (89.2%) 9% (51.7%)
(D.M. Kolesnikova et al., 2010)
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EW
50% (47.8%)
42% (30.9%)
6% (14.0%)
2% (5.5%)
Problems of Variable-Star Classification in Sky
Surveys
•The existing classification systems (GCVS etc.) are far
from being perfect;
•good software for automatic classification is not available;
•it is very tiresome to manually classify thousands of new
discoveries;
•in many cases, classification solely from the light curve is
impossible; additional information on the spectral type, Xrays, radial velocity variations is needed.
Beijing, 2012
Problems of Variable-Star Classification
Eclipses?
Pulsations?
Rotational variability of
a spotted star?
(V. Solovyov, A. Samokhvalov, B. Satovskiy,
2011, PZP, 11, 14)
Beijing, 2012
SPACE MISSIONS
The first space mission that
discovered many variable
stars: HIPPARCOS (ESA,
29-cm telescope, in operation
in 1989–1993)
About 5000 new variables
discovered
About 3000 new variables
added to the GCVS (others
remained insufficiently well
studied)
Just a 27-cm telescope!
Corot main goals:
– Asteroseismology
– Search for exoplanets
Corot mission launched
with a Russian rocket
(December 2006)
Beijing, 2012
Phase effects and an eclipse of an
exoplanet (I.A.G. Snellen et al., 2009,
Nature, 459, 543)
Kepler mission (NASA): a 95-cm telescope. Monitors a field at the
boundary of Cygnus and Lyra. Launched on March 7, 2009.
As of August 8, 2012 (no changes for several recent months…),
discovery of 2321 exoplanet candidates was announced; 74 of them
confirmed. Also announced are 2165 discoveries of eclipsing
variable stars. Stars with amplitudes of several thousandths of a
magnitude show reliable details on their light curves! New types of
eclipsing (+ pulsating) stars
Beijing, 2012
KEPLER Mission
42 CCDs, 2200х1024
~ 150 000 stars
Expected active time: 3.5 years
Able to detect a transit of an
earth-type planet of a solartype star at a 4σ level
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A Couple of New Kepler Var’s
Ampl = 0m.06
Ampl = 0m.006
(J. Greaves, 2010, PZP, 10, 7)
Beijing, 2012
KEPLER Observatory
Preliminary results:
Of ~ 150 000 program stars,
~ 60 000 are periodic variables,
~ 34 000 stars vary with poorly detectable periodicity or
aperiodically
(G. Basri et al., 2011, AJ, 141, 20)
Two thirds of all stars are variable for KEPLER precision
of photometry!
Beijing, 2012
GAIA mission (ESA). Expected launch: 2013 (as of August 2012,
the particular month, March, has recently disappeared from the
GAIA web site), with a Russian Soyuz-Fregat rocket to the L2
point. Astrometry, photometry. Is expected to discover several
million new variables down to the 20th magnitude (no better
prediction on the GAIA web site!). Two 1.45×0.5-m telescopes
Beijing, 2012
The planned Russian space experiment
“Lyra” on board the International Space
Station
A 50-cm telescope. Multicolor
photometry (catalog) of 100 to 400
million stars; the whole sky observed
some 20 times per year. The project is
being worked on at the Sternberg Institute
(Moscow)
Beijing, 2012
THE GENERAL CATALOGUE OF VARIABLE STARS
(GCVS) – SINCE 1946 ON BEHALF OF THE
INTERNATIONAL ASTRONOMCAL UNION
P.P. Parenago
(1906 – 1960)
B.V. Kukarkin
(1909 – 1977)
Beijing, 2012
P.N. Kholopov
(1922 – 1988)
The GCVS team
Beijing, 2012
Current contents of the GCVS:
about 45700 “named” variable stars (about 2150 will be added
before the end of 2012);
about 20000 “suspected” variable stars.
Compare to about 212000 variable stars in the AAVSO VSX.
So far, evaluation of information for the GCVS is still made on the
star-by-star basis by staff members of the GCVS. No software able
to provide classification of variable stars with uncertainties within
reasonable limits. WE ARE BEHIND THE FLOW OF
DISCOVERIES!
New classification system badly needed. However, it seems that new
discoveries change the general picture too strongly to introduce it
now!
Beijing, 2012
Final Remarks
• With full-scale results from Kepler (and then from similar missions)
approaching, everything we know about variability statistics will
have to be revised;
• The era of traditional variable-star catalogs is probably near its end,
despite traditional Argelander-style variable-star names being still
popular;
• A possible solution could be universal star catalogs, with variability
information as a minor part of them;
• The commission established by the IAU C27 six years ago to study
the future of variable-star catalogs apparently finds no brilliant ideas
how to proceed in order to solve this problem, really important for
the astronomical community.
• New ideas from the virtual-observatory community are welcome.
Beijing, 2012
Thank you!!!
Beijing, 2012