Download Present classification: Suggested

N.N. Samus
Institute of Astronomy (Russian Acad. Sci.),
Sternberg Astronomical Institute (Moscow University),
and Eurasian Astronomical Society
Modern Variable-Star
Classifications
7th Gamow Summer Astronomical School “Astronomy at
Crossroads of Science: Astrophysics, Cosmology, Radio
Astronomy, Astro-Biology”,
Odessa, Ukraine, August 7–11, 2007
WARNING: I am no expert in modern classification systems for
variable stars, though quite an expert in traditional ones and the
person responsible for collecting ideas for the new classification
systems to be approved by the IAU.
Classification begins as soon as people notice variable stars.
Old chronicles: “a guest star” (Nova, Supernova, comet), then
“Stella Nova”. 1596 – 1609: Fabricius discovers variability of
Omicron Ceti (this Greek designation is from Bayer, 1603, an
independent observation without noticing variations), and the star
gets a new name, Mira, the name still used for a type of variable
stars.
Odessa, August 7–11, 2007
The AAVSO light curve of Mira Ceti for the recent 60 years and the
Fabricius monument in Germany
Odessa, August 7–11, 2007
Very many variable-star types have been introduced. The GCVS
web site lists 114 types and subtypes of the classification system
used in the GCVS IV (1985) and subsequent Name Lists, but
some subtypes can be used additively, and the number of type and
subtype combinations actually encountered in the GCVS is still
larger.
Conflicting signals from the community concerning what to do
with the GCVS classification (“You have too many types to
understand, impossible to remember; from a type, you do not get a
clear idea of what the star you are dealing with can be like”; “Why
don’t you introduce the new type I have invented in the GCVS? I
have convincingly demonstrated it is physically meaningful”)
Odessa, August 7–11, 2007
The solution we propose:
Let us reduce the number of types in the GCVS and
make the classification simpler; let those wishing to
have subtle subdivisions among the stars of their
specific interest prepare specialized catalogs for
corresponding variable-star classes.
An additional requirement for a type to be used in the GCVS:
It should be possible to attribute stars to this type on the base of
observations comparatively easy to acquire in a routine study, not
from very detailed studies of each particular star.
Odessa, August 7–11, 2007
An old example of a very detailed morphological classification
for a particular type – that of H. Ludendorff (1928) for Miras:
α – ascending light-curve branch considerably steeper
than the descending branch
subtypes α1, α2, α3, α4 (from very flat minima to
narrower ones, shallower ascending branches)
β – ascending branch same steep as descending branch or
slightly steeper, generally symmetric curve
subtypes β1, β2, β3, β4 from sharp to flat maxima
γ – waves on ascending branch or double maxima
γ1 – waves on ascending branch
γ2 – double maxima
A Mira star probably can change its type in this classification!
The system has almost nothing to do with physics of Miras!
Odessa, August 7–11, 2007
Example of different approach – cataclysmic variables (among the
best-studied groups, with physically reasonable classification)
GCVS IV
Downes et al.
(archive)
GCVS
(suggested)
Dwarf Novae: UG, UGZ,
UGSS, UGSU
UG, UGZ, UGSS, UGSU,
UGWZ
UG, UGZ, UGSS, UGSU,
UGWZ, UG_ER
Novae: N, NA, NB, NC,
NR
N, NA, NB, NC, NR,
NRA, NRB
N, Nfh, NSym, Nr
Nova-like NL, AM (XM)
NL, NLV, UX, VY, AM,
DQ, CV, CBSS
CV, UXUMa, VY, AM,
DQ
– the approach is not that different, after all!
Odessa, August 7–11, 2007
Example of different approach – young irregular variables (a very
complex group, with old GCVS classification suggested by an
expert in this particular field, wishing to introduce more types)
GCVS IV
GCVS
(suggested)
FU, I, IA, IB, INA,
INB, INT, IT, IN(YY),
IS, ISA, ISB
I, TT, TTc, TTw,
HAeBe
– some simplification seems really possible!
Odessa, August 7–11, 2007
New automatic surveys: thousands of new variable-star discoveries,
necessity of reliable automatic classification methods.
Consider the associated problems using two of the best automatic
surveys, ASAS-3 and NSVS, as an example.
ASAS-3 (G. Pojmanski): small CCD cameras, calibrated V-band
magnitudes, southern hemisphere. A catalog of variables discovered
in the project: about 50000 variables, some 30000 of them new.
Variability types in the ASAS-3 catalog:
Ec, Esd, Ed; DSCT, RRc, RRab, DCEP, CW, Miras, ACV,
BCEP; Miscellaneous. Sometimes the pulsation mode is
indicated. The “type” Misc is the one most frequently used!
Odessa, August 7–11, 2007
Odessa, August 7–11, 2007
Problems with automatic period
determination and classification.
One of the Galaxy’s longestperiod fundamental-mode
Cepheids in the ASAS-3 lightcurve gallery
Same star: A.V. Khruslov, PZP,
2005, 5, No. 8
Odessa, August 7–11, 2007
An example of modern approach to ASAS-(1,2) variable-star
classification:
L. Eyer, C. Blake, 2005, MNRAS, 358, 30.
A completely automatic algorithm applied. Six major types:
eclipsing binaries, “sinusoidal curves”, Cepheids, smallamplitude red variables, SR, Mira stars.
Twelve types is the more detailed version:
~EA, EB, ~EW, eclipsing (more marginal cases), Cepheids,
Cepheids (with more marginal cases), LPVs, RR Lyrae
candidates, various case class, small amplitude variables,
SARVs, SRs, Miras.
The authors estimate the type classification error level to be
about 7 percent. In my opinion, first, this level is too high, and
second, the authors underestimate it.
Odessa, August 7–11, 2007
Here it seems to be relevant to make an important note
concerning all compact automatic classification systems.
Looking for variable stars: what for? If we are not mainly after
applied-science goals (like: We want to use this star for
spacecraft orientation, what can we expect from it?) and are
thinking about astrophysics, then we need 10000 new variable
stars to find 100 really interesting objects among them. It is these
100 stars that will never be classified correctly – and not isolated
as interesting cases – by existing automatic classification
systems.
Odessa, August 7–11, 2007
The NSVS project: a part of the ROTSE-I project, small CCD
cameras, northern hemisphere, instrumental R magnitudes. Though
potentially as rich in new variables as ASAS-3, the project has
announced 10 times fewer new variables so far.
It has been demonstrated by T.I. Ignatieva (MSci Thesis, Moscow
University, 2005) that some 18% of all stars announced by the
NSVS team as new Cepheids were actually non-eclipsing RS CVn
binaries with chromospheric activity.
Odessa, August 7–11, 2007
It is easy to recognize an eclipsing RS CVn binary:
A new RS CVn Algol discovered by A. Khruslov (Tula) in the NSVS data
Odessa, August 7–11, 2007
RS CVn binaries (eclipsing or not) with periods in the Cepheid
range are mostly quite detectable X-ray sources. Only the very
brightest Cepheids ( Cep,  Aql) are known
X-ray sources. This is the criterion used by Ignatieva but not
taken into account by the NSVS team.
Khruslov’s RS CVn star is the X-ray source
1RXS J060751.0+724636.
Odessa, August 7–11, 2007
A TYPICAL PROBLEM OF AUTOMATIC SKY SURVEYS
No. 1 varies!
Odessa, August 7–11, 2007
The general structure of the GCVS IV classification scheme
Large classes (groups of types):
1. Eruptive variable stars
2. Pulsating variable stars
3. Rotating variable stars
4. Cataclysmic (explosive and nova-like) variables
5. Close binary eclipsing systems
6. Optically variable close-binary sources of strong variable Xray radiation
These classes are just a way to group types; in our opinion, they
can be kept if slightly better described (e.g., remove close
from item 5, simplify item 6). Moreover, users ask for more
hierarchy in the classification!
Odessa, August 7–11, 2007
Our trial revision of the GCVS data for several southern
constellations show that type changes are not needed for most stars.
In the existing scheme, there can be combined types (like UV+BY),
meaning the same star simultaneously having properties of two or
more types.
We suggest to add one more symbol combining types, in the cases
when two or more classification options remain for the same star,
for example, EC|Ell, EC|RR (here EC means a contact eclipsing
binary, this is one of our suggestions from next slides). This symbol
will permit us to have more information in the main GCVS Table,
people do not read remarks very attentively. Moreover, it will
simplify moving stars from the suspected-variable catalogue to the
GCVS.
Odessa, August 7–11, 2007
For those knowing the current GCVS system and wishing to know
our plans of its modification:
PULSATING VARIABLES
Present classification:
Suggested:
ACYG
ACyg
BCEP, BCEPS
BCep (BCEPS seem not justified)
CEP
Cep (users suggest to have all
Cepheids, Pop I and II, combined at
a higher level)
DCEP, DCEPS, CEP(B)
DCep, DCep0, DCep1, DCepB01,
DCepB12
Remark: 0 – fundamental, 1 – 1st
overtone, 01 – fundamental plus
overtone, 12 – 1st and 2nd overtones.
For non-beat Cepheids, it is safer
not to indicate the mode yet
Odessa, August 7–11, 2007
PULSATING VARIABLES (CONTINUED)
Present classification:
CW, CWA, CWB
DSCT, DSCTC, SXPHE
L, LB, LC
M
PVTEL
RR, RRAB, RRC, RR(B)
RV, RVA, RVB
Suggested:
CW (period will also be given)
DSct (amplitude will also be given,
population membership is not
always obvious)
L, Lb (for red stars)
M (alternative idea: merge with
former SRA)
PVTel
RR, RR0, RR1, RRB01
RV, RVb (if the secondary wave’s
amplitude is at least equal to that of
the main oscillation)
Odessa, August 7–11, 2007
PULSATING VARIABLES (CONTINUED)
Present classification:
Suggested:
SR, SRA, SRB, SRC, SRS SR (the regularity level should be
indicated by the presentation of the
light elements; if a star is a
supergiant, it will be obvious from
its spectral type) (alternative: merge
former SRA with Miras or combine
all red stars at a higher level)
SRD
SRd (we feel not inclined to
introduce the UU Her type)
ZZ, ZZA, ZZB, ZZO
ZZ (subtype is contained in the
spectral type)
BLBOO
BLBoo (alternative: merge with
Cepheids)
GDOR
GDor
Odessa, August 7–11, 2007
PULSATING VARIABLES (CONTINUED)
Present classification:
RPHS
LPB or LBV
Suggested:
RPHS (rapidly pulsating hot
subdwards; we repeat our call for
suggestions of a better designation)
SPB
Odessa, August 7–11, 2007
ERUPTIVE VARIABLES
Present classification:
FU, I, IA, IB, INA, INB,
INT, IT, IN(YY), IS, ISA,
ISB
GCAS, BE
RCB
RS
SDOR
UV, UVN
Suggested:
I, TT, TTc, TTw, HAeBe
Remark: I is for irregulars with
doubts about their being young,
TTc for classical and TTw, for
weak-lined T Tauri stars, HAeBe
for Herbig Ae/Be stars. Alternative:
keep FU?
Be
RCB
Move to rotating variables
SDor
UV
Odessa, August 7–11, 2007
ERUPTIVE VARIABLES (CONTINUED)
Present classification:
WR
Suggested:
WR
New type: PP (a proto-planetary
object)
New type: dL (L dwarf), the causes
of variability not quite clear yet
Odessa, August 7–11, 2007
ROTATING VARIABLES
Present classification:
ACV, SXARI
ACVO
BY
ELL
FKCOM
PSR
R
Suggested:
ACV
roAp, ACV+roAp
BY; also should include
chromospherically active giants
Ell
FKCom
Psr
R
RS (earlier among eruptive)
Odessa, August 7–11, 2007
CATACLYSMIC VARIABLES
AND OTHER STARS WITH OUTBURSTS
Present classification:
N, NA, NB
NR
NC
NL
Suggested:
No subtype: CV
N, Nhf (final helium flash;
suggestions of a different
designation are welcome)
Nr, NSym (symbiotic Nova),
UGWZ (see below)
NSym
CV, UXUMa (“permanent
outburst”), VY (VY Scl type,
fadings from time to time)
Odessa, August 7–11, 2007
CATACLYSMIC VARIABLES
AND OTHER STARS WITH OUTBURSTS (CONTINUED)
Present classification:
Suggested:
SN, SNI, SNII
SN (to avoid introducing the current
complex classification)
AM (including XM from X-ray
variables), DQ (intermediate polars)
UG, UGSS, UGZ
UGSU, UGWZ (WZ Sge type,
extremely long supercycles, large
amplitudes), UG_ER (ER UMa
type, short supercycles and normal
cycles, small amplitudes; ideas of a
better abbreviation are welcome)
AM
UG, UGSS, UGZ
UGSU
Odessa, August 7–11, 2007
CATACLYSMIC VARIABLES
AND OTHER STARS WITH OUTBURSTS (CONTINUED)
Present classification:
Suggested:
ZAND
Sym, NSym
Odessa, August 7–11, 2007
ECLIPSING VARIABLES
(the description of the class should not mention close binarity)
Present classification:
Suggested:
E, EA, EB, EW, EP
E, EA, EC – contact (merging EB
and EW), EP
Remove from the classification,
indicate through the spectral type or
Remarks
If such a star has eclipses, give
notation like EA+RS, RS+EA
Remove from the classification;
as a rule, these types in the GCVS
are based on indirect evidence
PN, WD, WR
RS
AR, D, DM, DS, DW, K,
KE, KW, SD
Odessa, August 7–11, 2007
X-RAY VARIABLES
Present classification:
Suggested:
X, XB, XF, XI, XJ, XND,
AM (move to cataclysmics), X, XN,
XNB (approximately corresponds to
XNG, a B star orbiting a compact
object), Xlm (low mass), Xhm (high
mass), Xmq (microquasars). In this
class, advice from experts is
especially needed
Odessa, August 7–11, 2007
THANK YOU!
СПАСИБО!
ДЯКУЮ!
Odessa, August 7–11, 2007