Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

2.2 MB·English

by  Jose A. Caballero

Astron. Nachr./AN0000,No.00,1–13(0000)/DOIpleasesetDOI!
Finding the most variable stars in the Orion Belt with the All Sky Auto-
mated Survey
Jose´ A.Caballero⋆,M.Cornide,andE.deCastro
Departamento de Astrof´ısica y Ciencias de la Atmo´sfera, Facultad de F´ısica, Universidad Complutense de Madrid, E-
28040Madrid,Spain
0 Received05Sep2009,accepted04Jan2010
1
Publishedonlinelater
0
2
Keywords stars:variables:general—stars:pre-mainsequence—stars:oscillations—astronomicaldatabases:mis-
n
cellaneous—Galaxy:openclustersandassociations:OriOB1b
a
J Welookforhigh-amplitudevariableyoungstarsintheopenclustersandassociationsoftheOrionBelt.Weusepublic
5 datafromtheASAS-3PhotometricV-bandCatalogueoftheAllSkyAutomatedSurvey,infraredphotometryfromthe
2MASSandIRAScatalogues,propermotions,andtheAladinskyatlastoobtainalistofthemostvariablestarsinasurvey

] areaofside5degcentredonthebrightstarAlnilam(ǫOri)inthecentreoftheOrionBelt.Weidentify32highly-variable
R stars,ofwhich16hadnotbeenreportedtovarybefore.Theyaremostlyvariableyoungstarsandcandidates(16)and
S backgroundgiants(8),buttherearealsofieldcataclysmicvariables,contactbinaries,andeclipsingbinarycandidates.Of
. theyoungstars,whichtypicallyareactiveHerbigAe/BeandTTauristarswithHαemissionandinfraredfluxexcess,
h
wediscoverfournewvariablesandconfirmthevariabilitystatusofanothertwo.Someofthembelongtothewellknown
p σOrioniscluster.Besides,sixoftheeightgiantsarenewvariables,andthreearenewperiodicvariables.
-
o
r (cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
t
s
a
[ 1 Introduction denemissionlinesareothersignpostsusedtoconfirmvery

young ages in stars. Photometric variability in young stars
1
TheOriOB1bsubgroupassociation,mostlycoincidentwith ismostlyduetodark(cool)andbright(hot)spotsandflare
v
2 theasterismoftheOrionBelt,containsarichpopulationof activity,whicharerelatedtothestrengthenedmagneticac-
6 veryyoungstars(e.g.Haro&Moreno1953;Walker1969; tivyduetofastrotation,andinteractionswithcircumstellar
6 Warren & Hesser 1978; Brown et al. 1994; Sterzik et al. discs,suchasintense,variableaccretionepisodesoroccul-
0
1995;deZeeuwetal.1999;Bricen˜oetal.2001).Theyoungest tations(e.g.classicalworks:Joy1945;Walker1956;Herbig
.
1 regions, including Alnitak (ζ Ori), which illuminates the 1977 – theoretical works: Koenigl 1991; Collier Comeron
0 Flame Nebula (NGC 2024), and σ Ori, which illuminates &Campbell1993;Shuetal.1994–modernobservational
0
the Horsehead Nebula (Barnard 33 and IC 434), are to the works: Bouvier et al. 1993; Herbst et al. 1994; The´ et al.
1
: east of the Belt and have ages of 1 to 5Ma. Here lies the 1994;Hartmann&Kenyon1996;Hamiltonetal.2001;Eiroa
v
σ Orionis cluster, one of the most suitable sites for dis- etal.2002).
i
X covering and characterising substellar objects (Be´jar et al.
TheOrionNebulaClusterintheOriOB1dsubgroupas-
r 1999; Zapatero Osorio et al. 2002; Sherry et al. 2004; Ca-
a balleroetal.2007).ThepopulationofstarssurroundingAl- sociationhasbeenatraditionaltargetforstudyingthepho-
tometric variability of young stars (Jones & Walker 1988;
nilam (ǫ Ori) and Mintaka (δ Ori), to the west of the Belt,
Carpenteretal.2001;Herbstetal.2002;Stassunetal.2006;
are older (5–10Ma) and spread over a wider area than the
Parihar et al. 2009), but the surveys for variability in the
muchdenserσ Orioniscluster(Caballero&Solano2008).
OrionBeltarerelativelyscarce.Themostthoroughvariabil-
SurroundingtheBelt,thereisanotherdispersedpopulation
ity surveys in the Ori OB1 b association have been aimed
of 10–20Ma-old stars, mostly associated to the Ori OB1a
atthelow-masspre-mainsequencestarsandbrowndwarfs
subgroup association (Jeffries et al. 2006; Caballero 2007)
(Bailer-Jones & Mundt 2001; Zapatero Osorio et al. 2003;
and its agglomerates, such as the 25 Orionis group or the
Caballeroetal.2004,2006;Scholz&Eislo¨ffel2004,2005;
ηOrionisoverdensity(Bricen˜oetal.2007;Caballero&Di-
Bricen˜oetal.2005;Scholzetal.2009),whilethebrightest
nis2008).
variable stars were first recognised as early as the begin-
HαandX-rayemissionandinfraredexcessarethepri-
ningofthe20thcenturyandhavenotreceivedquiteatten-
mary features for the identification of very young stars as
tion.Onlyafew(multiple)young starsofimportantastro-
those in the Orion Belt. Optical and near-infrared variabil-
physical interest had been extensively monitored, such as
ity,cosmiclithiumabundances,surroundingjets,orforbid-
VV Ori (Miller Barr 1904; Struve & Luyten 1949; Terrell
⋆ Correspondingauthor:e-mail:[email protected] et al. 2007), σ Ori E (Walborn & Hesser 1976; Landstreet
& Borra 1978), or Mintaka AE–D (Stebbins 1915; Koch
(cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
2 Caballeroetal.:ThemostvariableASASstarsintheOrionBelt
1 0.6
0.5
0.5
0
g]
ma 0.4
0) −0.5 3 [
0 −
20 −1 AS 0.3
δ (J −1.5 V) AS00.2
σ(
−2
0.1
−2.5
0
86.5 86 85.5 85 84.5 84 83.5 83 82.5 82 7 8 9 10 11 12 13 14 15
α (J2000) V ASAS−3 [mag]
0
Fig.1 Spatiallocationofthe10029ASASsourcesinthe Fig.2 Diagram showing σ(V ) vs. V . ASAS sources
0 0
studiedareawithlightcurveswithmorethan40datapoints, above the dashed line are variable star candidates in this
markedwith(blue)smalldots.Northisup,eastistotheleft. work. X Ori is out of limits (V ∼ 12.7mag, σ(V ) ∼
0 0
The100ASASsourceswithpossiblevariablelightcurves, 1.4mag).
thethreeOrionBeltsupergiantstars(Alnitak,Alnilam,and
Mintaka, from east to west), and σ Ori are marked with
fornextphasesoftheanalysis.TheASASdatacoveredal-
(red) filled circles, big stars, and a small star, respectively.
mostsixyearsduringthefirstdecadeofthe21stcentury.
Note the blank strip where ASAS did not survey (between
Of the five available apertures (0, 1, 2, 3, 4), the “0”
Alnitak and σ Orionis’ declinations) and the overlapping
aperturephotometryseemedtoprovidebetterdata(i.e.less
between different ASAS pointings (at about the Mintaka’s
dispersion and number of grade “C” and “D” data points
declination).
–probablyuselessdataorwithoutphotometricvalueatall
duetobadpixels,frame-edgeandbrightstar/planetproxim-
& Hrivnak 1981). Many of the intermediate-mass T Tauri ity,orexcessivefaintness).AccordingtoPojman´ski(2002),
starsintheOrionBeltwithvariabilitydenominations (e.g. thefiveaperturescorrespondtodiametersizesoftheaper-
BG Ori, V505 Ori) were compiled by Fedorovich (1960) ture photometry from 2 to 6pixels; the “0” aperture corre-
and have never been monitored again. After a century of spondstothenarrowerphotometry(Pojman´ski,priv.comm.).
photometricsearchesintheregion,therearestillserendip- Fromthispointon,weusedonlytheJohnsonV magnitude
itous discoveries of bright, UX Orionis-, A-type, variable withtheASAS“0”aperturephotometry,whichweindicate
stars(Caballeroetal.2008). withthesymbolV .
0
Our aim is to find the most variable stars in the Orion Fig. 2 illustrates the selection of variable stars. It is a
Belt, giving especial emphasis to the young Herbig Ae/Be σ(V )vs.V diagraminwhichthevariablestarcandidates
0 0
(HAeBe) and T Tauri stars. To accomplish that, we have havelargervaluesofstandarddeviationσ(V )withrespect
0
usedtheASAS-3PhotometricV-bandCatalogueoftheAll to non-variable stars of the same average magnitude V .
0
SkyAutomatedSurvey(ASAS)1,whichis“alowcostproject ASASstarsbrighterthanV ≈8.5magareaffectedbysat-
0
dedicatedtoconstantphotometricmonitoringofthewhole urationinthedetectorandwerenotconsidered.Thelower
availablesky”(Pojman´ski1997,2002). envelopeatthenon-saturated,brightestendofthecloudof
data points in the diagram indicates the best photometric
accuracy of the system, which is of about 0.02mag. The
2 Analysis
obvious rise of the lower envelope at faint magnitudes is a
combinationofthestandarddeviations(root-mean-squares)
First,wecompiled63276ASASlightcurvesofobjectsin
from Poisson noise in the targets and from sky noise in
asquareofside5.0degcentredonAlnilam;seeFig.1.We
the photometric aperture (e.g. Irwin et al. 2007). The line
used the default parameters N > 4 data points and r <
usedastheselectioncriterionisthelowerenvelopeshifted
15arcsec (N is the number of data points within a circle
tolargerσ(V )sbymagnitude-dependentamounts(roughly
ofradiusrcentredonthecoordinatesofanASASsource). 0
0.06magatV ∼8.5–11.5mag,0.12magatV ∼12.5mag,
Ifnotforcertainblankstrip,thesurveyedareawouldhave 0 0
and0.18magatV ∼13.5mag).Thischoicewasrelatively
been 25deg2. To maximise the scientific return and min- 0
arbitrary: more or less restrictive selection criteria would
imise possible further troubles with light curves of poor
have given significantly less or more variable star candi-
quality, we discarded all ASAS light curves with N ≤ 40
dates,respectively.Thus,theusedselectioncriterionwasa
datapoints.Itleft10029lightcurves(16%)withN >40
compromisetominimisethenumberoffalsepositives(vari-
1 http://www.astrouw.edu.pl/asas/. ablestarcandidatesthatactuallydonotvary)andmaximise
(cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org
Astron.Nachr./AN(0000) 3
Table1 IdentifiedvariablesintheOrionBelt.
No. α2MASS δ2MASS V0 σ(V0) δV0 No⋆bs Spectral Name Class Variable
(J2000) (J2000) [mag] [mag] [mag] type
01 052859.57 –033352.3 13.621 0.412 0.055 190 ... V1159Ori Dwarfnova Known
03 053101.46 –032324.3 12.492 0.341 0.056 294 ... IRAS05285–0325 Giant New
06 053322.45 –030955.7 11.185 0.085 0.032 207 ... No.06 Unknown New
07 053748.79 –030748.7 10.780 0.101 0.021 286 ... IRAS05353–0309 Giant New
11 053209.94 –024946.8 11.581 0.524 0.032 191 F5–8Vpe RYOri HAeBe Known
12 053833.68 –024414.2 12.885 0.368 0.054 187 K4e TXOri TTauri Known
13 053825.87 –024351.2 13.059 0.356 0.054 142 K3e TYOri TTauri Known
14 054354.26 –024335.4 11.628 0.135 0.032 222 ... 2M054354–0243.6 Contactbinary Known
15 053939.99 –024309.7 13.246 0.246 0.054 197 ... RWOri TTauri Known
18 053848.04 –022714.2 13.340 0.295 0.053 224 K7e+M: Mayrit528005AB TTauri New
21 053620.91 –021057.6 12.607 0.192 0.056 252 F3e PQOri HAeBe Known
29 053738.67 –014616.6 12.752 1.441 0.054 179 M8–9III: XOri Giant Known
30 053756.59 –014050.3 10.734 0.250 0.021 273 ... IRAS05354–0142 Giant New
33 053002.89 –013005.3 12.786 0.263 0.056 176 ... No.33 Unknown New
36 053425.82 –012106.5 12.667 0.325 0.055 170 ... V469Ori TTauri Known
41 052653.53 –010902.3 13.478 0.480 0.057 144 ... KisoA–0903135 TTauri? New
43 053759.04 –010552.8 13.554 0.371 0.054 200 ... V993Ori TTauri? Known
46 053126.41 –005833.1 10.454 0.076 0.021 192 F0 HD290509 Unknown New
48 053945.65 –005550.9 10.934 0.075 0.021 203 ... GSC04767–00071 TTauri? Known
51 053624.29 –004212.0 13.399 0.388 0.056 227 K3e PUOri TTauri Known
53 053448.91 –003716.7 13.384 0.298 0.056 178 ... V472Ori TTauri? Known
54 052724.67 –003511.2 11.031 0.134 0.033 184 ... IRAS05248–0037 Giant New
55 053543.27 –003436.7 12.411 0.278 0.057 246 K4e StHA48 TTauri New
60 052634.28 –001927.2 12.353 0.137 0.056 181 ... No.60 Giant New
65 053628.55 +000445.7 11.987 0.131 0.056 257 ... No.65 Unknown New
66 054329.25 +000458.9 11.459 0.513 0.032 202 F0? GTOri Giant Known
70 054418.80 +000840.4 8.906 0.061 0.019 204 A7IIIe V351Ori HAeBe Known
72 054611.86 +003225.9 13.390 0.439 0.053 167 ... VSSVI–32 Unknown New
73 054159.81 +003527.1 12.698 0.435 0.053 185 ... No.73 Unknown New
74 053642.64 +003834.3 11.010 0.101 0.033 254 A2 HD290625 HAeBe New
75 053347.85 +005536.3 10.433 0.166 0.021 181 ... IRAS05312+0053 Giant New
78 052817.85 +011006.1 11.219 0.165 0.033 173 F8–K0e StHA40 TTauri Known
the number of actual variable stars, but always keeping a correspond to the best and mean data, respectively2. Be-
maneagablenumberofobjectstobefollowedup. cause of the large ASAS pixel size (of about 15µm) and
typicalfullwidthathalfmaximum,ofnolessthan1.4pixels
Therewere100ASASlightcurvesabovetheselection
(Pojman´ski2002),wediscardedallvisualbinariesofroughly
criterion in Fig. 2. We were able to identify the 2MASS
thesamebrightnessseparatedbylessthanabout20arcsec.
(Skrutskie et al. 2006) and USNO-B1 (Monet et al. 2003)
Besides, we also discarded relatively faint variable candi-
possiblestellarcounterparts of99ofthem.Theunidenfied
datesatlessthan1arcmintoverybrightstars,includingAl-
ASASsourcewas054200–0154.7(V =13.167mag,σ(V )
0 0
nilam,Mintaka,andσOri,whichareseenbythenakedeye
=0.245mag,N =49),whichisactuallyabrightspotin
obs
and lead to a high sky background. After these removals,
NGC2024.Forthevisualidentification,weusedtheAladin
wekept32variablestarswhoselightcurveswerelikelynot
interactiveskyatlas(Bonnareletal.2000).Theactualnum-
contaminatedbyotherstars.The32lightcurvesareshown
ber of stars with light curves was 78, because there were
inFigs.A1toA4.
21 variable star candidates with two corresponding light
curves.Theseparateddatasets(withidenticalassociatedco- The identification number, 2MASS coordinates, aver-
ordinates and magnitudes within error bars) correspond to ageV0 magnitude,standarddeviationσ(V0),meanerrorof
thesamestarindifferentobservedfields(Pojman´ski2002). magnitudeδV0,andnumberoffinallyusedlightcurvedata
points, N⋆ , of the 32 identified variable stars are listed
WerevisitedtheASASdataforthe78starsbyretrieving obs
in Table 1. The ratios between the standard deviations and
alldatapointswithqualitygrades“A”and“B”inacircleof
mean errors vary between ∼2.5 and 27; the expected ratio
radiusr=15arcseccentredonthestars,andmergingthem
intoauniquelightcurve.“A”and“B”qualitygrades,which
2 Thequalitygrades“A”and“B”ofanewASASframedependson
aretabulated by the ASAS catalogue and derived fromthe
theaveragedispersionbetween‘old’and‘new’magnitudesforstarsinthe
averagephotometricqualityoftheframeforeachaperture, range8–11mag(Pojman´ski,priv.comm.).
www.an-journal.org (cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
4 Caballeroetal.:ThemostvariableASASstarsintheOrionBelt
Table2 Identifiedvariableswithpowerspectrummaxima
1 largerthan500mag2.
0.9
No. Power P Name Remarks
0.8 [mag2] [d]
s0.7
ar 01 767.19 44.345 V1159Ori P =44.2–46.8d
st0.6
of 03 1785.4 78.226 IRAS05285–0325 Newperiodic
on 0.5 11 632.39 600.38 RYOri Noclearpeak
acti0.4 29 8779.7 416.05 XOri P =424.2±1.8d
Fr0.3 30 913.68 373.31 IRAS05354–0142 Newperiodic
66 1671.2 920.32 GTOri Pulsating
0.2
0.1
0 2
101 102 103 104
Power spectrum maximum [mag2] 1.8
Fig.3 Cumulative distribution function of power spec- 1.6
trum maxima of the light curves of the 32 identified vari- 1.4
ablesintheOrionBelt.Starstotherightofthedashedver- g] 1.2
ticallineatpowerspectrumof500mag2 areclassifiedhere ma
asprobableperiodicvariablestars. K [s 1
J− 0.8
0.6
for a non-variable star should be lower than 2 (e.g. Bailer-
0.4
Jones&Mundt2001).InTable1,wealsoprovidethespec-
0.2
traltypefromtheliterature(ifithaseverbeengiven),name,
variabilityclass(seeSection3),andifthevariabilitystatus 0
−2 0 2 4 6 8 10 12
V −J [mag]
wasknownornot.Forthosestarsthathaveneverbeenmen- 0
tioned in the literature, we use the nomenclature “No. X”,
Fig.4 Optical-infraredcolour-colourdiagram(J−K vs.
s
whereXistheidentificationnumber.
V −J).Filled(red)stars:newvariableyoungstars;filled
0
ForatypicalnumberoflightcurvedatapointsofN⋆ ∼
obs (red) circles: previously known variable young stars; filled
200 and a temporal coverage of almost six years, one may
(red) squares: variable young star candidates; open (blue)
derivethattherewasanASASvisitevery∼11dforeachof
circles:variablegiants;open(blue)up-triangle:dwarfnova
the32stars.Actually,thetypicaltimeintervalbetweencon-
(V1159 Ori); open (blue) down-triangle: contact binary
secutive ASAS visits was shorter because there were long
(2M054354–0243.6); open (blue) squares: other new vari-
non-observinggapswithoutdata.Themediantimeinterval
ablestars.
betweenconsecutiveASASvisitswas2.0–3.0d,depending
on the star. Approximately 15–20, 20–33, 65–85, and 85–
95%ofthetimeintervalswereshorterthan1,2,5,and10d, average non-colour corrected flux densities with qualities
respectively,andonlyinfourcases,coincidentwiththefour “3”or“2”(highandmoderatequalities,respectively).While
Australsummers,thetimeintervalswerelongerthan100d. allthe32starshaveanear-infraredcounterpartinthe2MASS
Weperformedarutinarytime-seriesanalysisonthe32 catalogue, only 12 stars were identified in the IRAS cata-
lightcurvesbyapplyingtheScargle(1982)procedure.Fig.3 logues (e.g. IRAS catalogue of point sources, version 2.0;
showsthecumulativedistributionfunctionofthemeasured IPAC 1986). Furthermore, only one star, the A7IIIe Her-
maximaofpowerspectrum.Roughly85%ofthestarshave big Ae/Be star V351 Ori, has high/moderate quality mea-
powerspectrummaximalowerthan500mag2,wherethere surements at the four IRAS passbands at 12, 25, 60, and
seems to be an inflection point in the cumulative distribu- 100µm.Acolour-colourdiagramcombiningASASoptical
tion function. The other 15% (6) of the stars with larger and2MASSnear-infraredmagnitudesisshowninFig.4.
powerspectrummaximaaregiveninTable2andwereclas- Besides,wealsocollectedpropermotionsfromTycho-2
sifiedbyusasprobableperiodicvariablestars.Weprovide (Høgetal.2000),PPMX(Ro¨seretal.2008),andUSNO-B1
periods for two previously known periodic variable stars forthe32stars.Giventhatonlyafewofthemhaveappre-
(V1159 Ori and X Ori) consistent with those in the liter- ciable proper motions, we do not list them, but are men-
ature, and found probable periods for two previously un- tionedinSection3whenappropriated.
knwon variable giant stars (with IRAS denomination), but Finally, only 13 stars have variable star designations,
failedtofindanyreliableperiodictyforRYOriandGTOri. and there were suspects of variability for other three stars.
ThesixofthemwillbestudiedindetailinSection3. Besides,animportantfractionofthetargetshavealsobeen
Weperformedacompilationofadditionalinfrareddata tabulated as variable stars of the Southern Hemisphere by
by collecting JHK magnitudes from 2MASS and IRAS Pojman´ski (2002), to which our work complements. Next,
s
(cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org
Astron.Nachr./AN(0000) 5
Table3 Infraredphotometryofidentifiedvariables.
No. J H Ks F12 F25 F60 F100
[mag] [mag] [mag] [Jy] [Jy] [Jy] [Jy]
01 13.817±0.027 13.781±0.046 13.675±0.050 ... ... ... ...
03 6.097±0.019 5.083±0.027 4.639±0.021 1.08±0.08 0.39±0.04 <3 <20
06 8.295±0.034 7.552±0.024 7.368±0.026 ... ... ... ...
07 5.590±0.021 4.665±0.076 4.222±0.033 1.09±0.07 0.47±0.08 <0.9 <30
11 9.444±0.023 8.885±0.055 8.277±0.031 0.75±0.09 0.71±0.09 <2 <20
12 10.131±0.026 9.280±0.024 8.666±0.024 0.38±0.04 0.50±0.07 <0.7 <40
13 10.445±0.027 9.726±0.024 9.311±0.028 ... ... ... ...
14 10.240±0.026 9.943±0.026 9.816±0.021 ... ... ... ...
15 10.647±0.027 9.920±0.023 9.530±0.019 ... ... ... ...
18 10.156±0.023 9.463±0.026 9.187±0.019 ... ... ... ...
21 11.303±0.022 11.065±0.028 10.979±0.023 ... ... ... ...
29 2.322±0.292 1.379±0.306 0.861±0.346 96±4 49±7 6.0±0.9 <20
30 5.152±0.018 4.608±0.076 3.972±0.320 2.0±0.2 0.63±0.07 <2 <40
33 11.340±0.024 10.878±0.025 10.756±0.021 ... ... ... ...
36 10.655±0.023 9.647±0.030 8.759±0.021 ... ... ... ...
41 11.547±0.027 10.652±0.027 9.898±0.019 ... ... ... ...
43 10.846±0.027 9.955±0.024 9.355±0.027 ... ... ... ...
46 9.457±0.023 9.247±0.023 9.133±0.021 ... ... ... ...
48 8.589±0.023 7.933±0.055 7.797±0.027 ... ... ... ...
51 10.536±0.023 9.551±0.033 8.764±0.019 <0.4 0.38±0.05 <3 <20
53 10.860±0.022 10.043±0.026 9.538±0.019 ... ... ... ...
54 5.206±0.017 4.225±0.202 3.911±0.258 1.48±0.09 0.49±0.04 <5 1.7±0.3
55 10.243±0.021 9.509±0.033 9.061±0.019 ... ... ... ...
60 7.508±0.023 6.596±0.029 6.280±0.021 ... ... ... ...
65 10.762±0.024 10.447±0.025 10.054±0.019 ... ... ... ...
66 9.802±0.027 9.043±0.025 8.219±0.026 0.87±0.13 1.02±0.17 <5 <40
70 7.950±0.020 7.504±0.040 6.846±0.026 1.16±0.07 4.1±0.2 26±3 21±3
72 10.936±0.024 10.046±0.023 9.448±0.019 ... ... ... ...
73 10.448±0.023 9.818±0.023 9.351±0.019 ... ... ... ...
74 10.459±0.024 10.342±0.024 10.317±0.023 ... ... ... ...
75 6.304±0.026 5.375±0.027 5.091±0.020 0.47±0.03 <0.2 <0.4 <20
78 9.422±0.023 8.825±0.040 8.366±0.018 0.41±0.06 0.67±0.06 0.47±0.05 <1.1
weclassifythe32variablestarsbasedonspectroscopic,as- Besides,sixofthestarsinthisclassdisplayX-rayemission,
trometric,andphotometriccriteria. andothersix,infraredfluxexcess.OnlythethreeσOrionis
members are known to simultaneously display Hα and X-
rayemissionsandinfraredfluxexcess.
3 Identifiedvariablestars
RYOri(No.11). Itisawellinvestigated,emission-line
3.1 HAeBeandTTaurivariablestars
staroftheOrionpopulationattheboundarybetweenHAeBe
3.1.1 Previouslyknownvariableyoungstarsand andTTauristars(e.g.Haro&Moreno1953;Herbig&Bell
candidates 1988; Yudin & Evans 1998; Eiroa et al. 2001; Mora et al.
2001;Herna´ndezetal.2004;Acke&vandenAncker2006).
This class is mostly made of probable accreting T Tauri Itsphotometricvariabilitywasdetectedveryearly(Picker-
stars with intense Hα emission. Of the nine Hα emitter ing1904).AccordingtoBibo&The´(1991),itisaUXOri-
stars,threebelongtotheσOrioniscluster(TXOri,TYOri, typestarwithacolourreversalinthecolour-magnitudedi-
RW Ori), three have been associated to the Alnilam and agram, indicative of an edge-on disc. The disc of RY Ori
Mintakayoungstarpopulations(V469Ori,PUOri,V472Ori),isalsodetectedbecauseofitslong-time-knowninfraredex-
andthreehavenotbeenlinkedtoanyyoungregioninpartic- cess(Cohen1973;Glass&Penston1974;Weintraub1990;
ularbutarebrightstarsattheboundarybetweenHAeBeand Weaver & Gordon 1992). Its photometric variability in the
TTauristars(RYOri,V351Ori,StHa40–twoofthemmay ASAS lightcurve is obvious, with small mean photometric
haveedge-ondiscs).Thetruenatureoftheotherthreenon- errorswithrespecttothepeak-to-peakamplitudefrom10.8
Hα emitter stars (PQ Ori, V993 Ori, GSC 04767–00071) to 13.0mag (δV = 0.032mag). RY Ori is one of the six
0
shouldbeinvestigatedwithfurtherspectroscopicanalyses. identified variable stars with power spectra maxima larger
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6 Caballeroetal.:ThemostvariableASASstarsintheOrionBelt
ima at about V ∼ 12.5 and 14.0mag. Remarkably, the
0
700
TX Ori light curve displayed an apparent dimming for he-
liocentricJulianday3 HJD>3500.
600
500 RW Ori (Mayrit 931117, No. 15). It is another mem-
2g] berintheσ Orioniscluster,butitismuchlessknownthan
a400
m thestarsabove.ItsphotometricvariabilityandHαemission
er [ werefirstdetectedbyPickering(1906)andHaro&Moreno
w300
o
P (1953), respectively. Afterwards, it has been only investi-
200 gatedbyFranciosinietal.(2006–withXMM-Newton,Her-
na´ndezetal.(2007–withSpitzer),andCaballero(2008).Its
100
ASASlightcurvevariedbetweenV ∼12.8and14.0mag
0
(theoutlierdatapointisprobablyunreliable).
0
10−1 100 101 102 103 104
Period [d]
PQOri(No.21). Inthediscoverypaper,McKnelly(1949)
10.5 classified the star as a rapid, irregular variable with an ob-
servedrangeofvariabilityof12.5–13.5mag(photographic
11 magnitude).Althoughitslightcurvedisplayedmanymax-
ima and minima, he was unable to determine “any sem-
11.5 blance of periodicity”. Herbig & Kameswara Rao (1975),
g] Cohen & Kuhi (1979), and Herna´ndez et al. (2004) mea-
a
m 12 suredF0,F5:,andF3.0±1.5spectraltypesandobservedno
[0
V emissionlines.However,whilethefirstauthoursclassified
12.5 itasastarintheOrionpopulation,Herna´ndezetal.(2004)
didnotfindsignificantdifferencesfromF3main-sequence
13 stars nor near infrared excess, and categorized it as an ob-
jectwithuncertainevolutionarystatus.Thevariabilitypat-
13.50 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 ternsintheASASlightcurveofPQOri,althoughranging
Phase betweenV ∼12.3and13.3mag,donotresemblethoseof
0
otheryoungstarsinthiswork,anditsJ−K colourisquite
Fig.5 Periodogram of the ASAS light curve (top) and s
blue with respect to other early F stars in Ori OB1 b. As a
phase-folded light curve of RY Ori to the period P =
result,itsfielddwarfnatureseemstousmoreplausible.
600.38d(bottom).
V469Ori(No.36). Itisanemission-linestarwithX-ray
than 500mag2 (Table 2 – actually, it is the star with the
emission(Haro&Moreno1953;Wiramihardjaetal.1989;
lowestpowerspectrummaximum).Theperiodogramofthe
Nakanoetal.1999).AccordingtoCaballero&Solano(2008),
ASASlightcurve,displayedinFig.5,showsnoclearpeak,
the star is a member in the young Ori OB1 b stellar popu-
withanumberofpowermaximaincreasingtowardslonger
lationsurroundingAlnilam,andisproablyassociatedtothe
periods. The phase-folded light curve at the period of the
[OS98]29J,[OS98]29H,and[OS98]29Kremnantmolec-
heighestpeak,atP ∼600d,doesnotshowanyevidenceof
ularclouds(Ogura&Sugitani1998).BasedonitsV −K
0 s
realperiodicity.Actually,fromthefull-lengthlighcurvein
colour and the empirical scale of effective temperatures of
Fig.A1,thetimescaleoftheirregularvariabilityofRYOri
main-sequence stars of Alonso et al. (1996), and extrapo-
isoftheorderofafewdays,justlikemanyconfirmedyoung
latingittothepre-mainsequence,V469Oriislikelyalate
starsinthiswork.
GeorearlyKestar.ItsASASlightcurvelookslikethoseof
otherTTauristars.
TXOri(Mayrit521199,No.12)andTYOri(Mayrit489196,
No.13). Theyaretwoclose(ρ∼40arcsec)pre-mainse-
V993Ori(No.43). Itisalong-time-knownvariablestar
quencestarsintheσOrionisclusterthathaveappearedina
discovered by Luyten (1932). Caballero & Solano (2008)
numberofyoungandemission-linestarcatalogues(Herbig
classifieditasaprobablememberoftheOriOB1byoung
& Kameswara Rao 1972; Cohen & Kuhi 1979; Herbig &
stellar population surrounding Alnilam. It has a very red
Bell 1988; Ducourant et al. 2005). As in the case of many colour J − K = 1.26±0.04mag for its brightness (H =
s
variablestarsinthiswork,theywerediscoveredasvariable
stars by Pickering (1904). Both TX Ori and TY Ori have 3 The values of heliocentric Julian day used in the Figures are those
been subject of comprehensive studies and data compila- tabulatedbytheASAScatalogue.Actually,theyarenotheliocentricJulian
days HJD, but the HJD minus the constant 2450000.0 (do not confuse
tionsbyOliveira&vanLoon(2004)andCaballero(2008).
withtheconstantusedtotransformtheJuliandayintothemodifiedJulian
Theirlightcurvesarequitesimilar,withminimaandmax- dayMJD,whichis2400000.5).
(cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org
Astron.Nachr./AN(0000) 7
9.82±0.02mag),whichmayindicatethepresenceofacir- (van den Ancker et al. 1998; Marconi et al. 2001; Ripepi
cumstellar disc or, alternatively, that it is a background gi- et al. 2003). The pre-main sequence nature of the star is
ant star. It may be the optical/near infrared counterpart of supportedbythepresenceofHαinemission,apronounced
IRASZ05354–0107,asourceintheIRASFaintSourceRe- inversePCygniprofile,SIλ1296A˚ andOIλ1304A˚ lines
jectCatalog(Moshir1992).Thereisnospectroscopyavail- inemission,andinfraredexcess(Valentietal.2000andref-
able to confirm or discard its possible T Tauri status. The erencesabove).WithV ≈8.91magand20–30Jyatthe60
0
largepeak-to-peakamplitudeofitslightcurveofV ∼13.0 and 100µm IRAS passbands, it is by far the brightest star
0
tofainterthan14.5mag,althoughshedslightonthephoto- in our sample at all wavelengths, but also the less variable
metricvariabilityofV993Ori,isnotconclusive. one. However, the amplitude of variability, between V ∼
0
8.80 and 9.15mag, is slightly larger than previously mea-
sured.Itmaybeduetoourlong(ASAS)temporalcoverage,
GSC04767–00071(No.48). Schirmeretal.(2009)clas-
probablylongerthananyotherpreviousmonitoring.
sifieditasachromosphericallyactivestarsuspectedofvari-
abilityintheROTSE-1database.ThestarGSC04767–00071
isprobablyassociatedtotheX-raysource1RXSJ053944.7– StHa40(No.78). ItwasfirstlistedintheHα-emission
005612(Vogesetal.1999)andhasaverylowPPMXproper starcataloguesofMacConnell(1982)andStephenson(1986)
motion,of(µ cosδ,µ )=(–6±2,–9±2)masa−1.Theop- and followed-up afterwards by Downes & Keyes (1988),
α δ
ticalandnear-infraredphotometrysupportsmembershipin Torresetal.(1995),Gregorio-Hetem&Hetem(2002),and
Ori OB1 b. It may be a very young solar analog. The am- Maheswaretal.(2003).StHa40isaTTauristarwithvari-
plitudeofphotometricvariabilityofitsASASlightcurve,of able spectral type (from F8, through G2 and G5, to K0),
V ∼10.8to11.1mag,isrelativelysmall. variableHαemission(frompEW(Hα)=–14.5A˚ toafaint
0
absorption),lithiumabsorption(frompEW(LiI)=+0.13to
+0.33A˚),andradialvelocity(indicativeofpossiblespectral
PUOri(No.51). Itisapre-mainsequencestarnearthe
binarity). Besides, Gregorio-Hetem & Hetem (2002) asso-
Alnilam supergiant with Hα in strong two-lobe emission
ciated StHa 40 to a ROSAT X-ray source and derived ba-
(Haro & Moreno 1953; Herbig & Kameswara Rao 1972;
sic stellar and circumstellar parameters. Maheswar et al.
Cohen&Kuhi1979;Wiramihardjaetal.1989),photomet-
(2003) estimated a magnitude difference ∆V ∼ 1.6mag
ricvariability(Fedorovich1960;Bricen˜oetal.2005),mid-
between two optical spectra taken almost three years apart
infraredfluxexcessattheIRASpassbands(Weintraub1990;
and after comparison with spectro-photometric standards.
Weaver&Jones1992),andforbiddenemissionlines([OI]
TheHαlinewasinemission[absorption]whenthestarwas
λ6300.3A˚; Hirth et al. 1997). It has a very red colour of
brighter,V ∼10.9mag[fainter,V ∼12.5mag].However,
J−K =1.77±0.03mag(Caballero&Solano2008).From
s whilethebrightestMaheswaretal.(2003)’sestimationfor
our light curve, PU Ori is an irregular variable with mini-
V agreesverywellwithourlightcurve(fromwerewemea-
mumandmaximummagnitudesV ∼12.5and14.5mag.
0 sure V ≈ 11.0mag), none of the 173 StHa 40 data
0,bright
pointscoveringalmostsixyearswerefainterthanV ≈
0,faint
V472 Ori (No. 53). It is an Hα emitter star (Haro & 11.8mag.
Moreno 1953; Wiramihardja et al. 1989) of known photo-
metricvariability(Fedorovich1960;Cieslinskietal.1997).
3.1.2 Previouslyunknownvariableyoungstars
Itmaybetheoptical/nearinfraredcounterpartofIRASZ05322–
0039.V472OriisaprobablememberintheMintakaclus- Ofthefourstarsinthisclass,onlytwo(Mayrit528005AB
ter(Caballero&Solano2008).ItsASASlightcurvehasa andStHa48)haveuncontrovertiblesignpostsofyouth.The
peak-to-magnitudelargerthan1mag. othertwostars(KisoA–0903135andHD290625)havenot
beenwellinvestigatedyetandmaynotbelongtotheyoung
OrionBeltstellarpopulation.
V351Ori(No.70). ItisaHAeBeA7IIIevariablestarof
δ ScutitypediscoveredbyHoffmeister(1934).Ithasbeen
investigatedindetail,especiallyafterKovalchuk(1984)ob- Mayrit 528005 AB (No. 18). It is a hierarchical triple
served a flare-like event on its light curve at the UBVR systemintheσOrioniscluster,madeofaclosebinary(ρA−B =
bands (Wouterloot & Walmsley 1986; Sterken et al. 1993; 0.40±0.08arcsec)resolvedwithadaptiveopticsatρAB−C ∼
Rosenbush 1995; Marconi et al. 2000; Balona et al. 2002; 7.6arcsectothelow-massstarMayrit530005(SOriJ053847.5–
Vieria et al. 2003). It has been proposed that a temporar- 022711; Caballero 2005, 2009). The binary primary has a
ilystrongaccretionofmatterontothestarorextinctionby cosmic lithium abundance (Zapatero Osorio et al. 2002),
circumstellardustcloudstakesplacetoexplaintheremark- double-peak Hα (Caballero 2006), and strong X-ray emis-
ableV351Orichangeofbehaviourfrom“thatofa[HAeBe] sions (Wolk 1996; Fraciosini et al. 2006; Caballero et al.
starwithstrongphotometricvariations[...]tothatofanal- 2009),andanspectralenergydistributiontypicalofclassII
most non-variable star” (van den Ancker et al. 1996). The objects(Herna´ndezetal.2007).TheASASlightcurveshows
main period of pulsations of V351 Oriis only of the order variability between V ∼ 13 and 14mag, and an apparent
0
of 0.06d with a peak-to-peak amplitude of about 0.1mag seriesofbrighteningsatHJD∼3000.
www.an-journal.org (cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
8 Caballeroetal.:ThemostvariableASASstarsintheOrionBelt
Kiso A–0903 135 (No. 41). It is an emission-line star
9000
only referenced once by Kogure et al. (1989), who mea-
sured a weak Hα emission intensity and placed it in the 8000
Orionregion.Itsoptical(DENIS;Epchteinetal.1997)and
7000
near-infrared(2MASS)photometryandnullpropermotion
6000
(withinerrorbars;USNO-B1)areconsistentwithmember- 2g]
isthiips oinnethoefOthrieOmBo1stbvaarsisaobclieatsitoanr.sWinitthheσVst0ud=y0..W48h0ilmeaigts, wer [ma45000000
brightest magnitude is V ∼ 12.8mag, the faintest one is o
0 P
V ∼15.0magorfainter. 3000
0
2000
StHa 48 (No. 55). It is a K4-type T Tauri star with Hα 1000
in emission and Li I in absorption (Stephenson 1986; Ma- 0
heswar et al. 2003; Caballero & Solano 2008). The star, 10−1 100 101 102 103 104
Period [d]
whichislocatedinthesurroundingsofAlnilam,hasawide
amplitudeofvariability,withmaximumandminimumbright- 9
eness at V ≈ 11.9 and 13.3mag, respectively, and time
0
scalesofvariationofafewdays. 10
11
HD290625(No.74). ItisanA2starclassifiedasaprob-
able member in the young stellar population of Ori OB1 b ag]
m 12
(Guetter1979;Nesterovetal.1995).TheASASlightcurve [0
displayed variations between V ≈ 10.8 and 11.3mag, ap- V
0
13
proximately.TheTycho-2and2MASSphotometryandthe
lowpropermotion,oflessthan4masa−1(Tycho-2,PPMX,
14
USNO-B1),areconsistentwiththespectraltypeandalong
heliocentricdistance.Besides,lifesofA2starsarerelatively
15
short, which confirm the HD 290625 youth. However, the 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Phase
starisacoupleofmagnitudesfainterthanexpectedfor“nor-
mal”A2Orionstarsatd ∼0.4kpc.Insteadofresortingto Fig.6 Same as Fig. 5, but for X Ori and a period P =
another young population in the far background of Orion, 416.05d.
ofwhichthereisnoevidence,weproposethatHD290625
is a variable HAeBe star with a scattering edge-on disc in
MidcourseSpaceExperiment(8.3–21.3µm;Kraemeretal.
the Orion complex, just like UX Ori or the σ Orionis star
2003).Therewerealsoonlythreestarspreviouslyclassified
StHa50(Mayrit459340–The´ etal.1994;Caballeroetal.
asgiants:XOri,GTOri,andIRAS05354–0142(forwhich
2008)or,alternatively,abright,blue,subdwarf(therehave
variability had not ever been proposed). Therefore, in this
been previous detections of such objects in the area: Ca-
workwepresentsixnewvariablegiants.Besides,wemea-
ballero&Solano2007;Vennesetal.2007).
sureperiodsofphotometricvariability(withmaximaofthe
powerspectrumabove500mag2)between78and920dfor
3.2 Variablebackgroundgiants
four of the eight giants, while only one, X Ori, had been
reportedbeforetodisplayperiodicity.
Unfortunately,becauseoftherelativeresemblancebetween
the spectral energy distributions of distant giant stars with
extendedcoolenvelopesandofyoungstarswithdeveloped
3.2.1 Knownbackgroundgiants
discs (due to the common strong infrared flux excess), gi-
antstarssometimescontaminatelistsofmembercandidates X Ori (No. 29). This giant or superginat star was the
in star-forming regions. For example, the bright (in the in- reddest object in the Alnilam-Mintaka area studied by Ca-
frared)giantstarIRAS05358–0238wasonceclassifiedasa ballero & Solano (2008), but is located at about twice the
ClassIobjectintheσOrioniscluster(Oliveira&vanLoon heliocentricdistancetotheOriOB1association(Juraetal.
2004;Herna´ndezetal.2007;Caballero2008).Sincethesur- 1993).ItisanM8–9-typeMiraCetivariablefoundbyWolf
veyed area in this work is rich in star-forming regions (in- (1904)withP =424.75±1.77d(Templetonetal.2005)and
cludingσOrionis),wehadtobecarefulwithdisentangling silicate dust emission (Sloan & Price 1998; Speck et al.
bothpre-mainsequenceandgiantstarpopulations. 2000). In particular, the 9.7 and 18µm silicate dust fea-
Oftheeightidentifiedvariablebackgroundgiants,only tureoriginatesfromthecircumstellarenvelopesofoxygen-
one (No. 60) has no IRAS excesses or were not detected richasymptoticgiantbranchstars(Kwoketal.1997).From
with the Spatial Infrared Imaging Telescope onboard the ourperiodogram(Fig.6),therearetwoclearpeaksatP ≈
(cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org
Astron.Nachr./AN(0000) 9
1800 1000
1600 900
800
1400
700
1200
2g] 2g] 600
ma1000 ma
wer [ 800 wer [ 500
o o 400
P P
600
300
400
200
200 100
0 0
10−1 100 101 102 103 104 10−1 100 101 102 103 104
Period [d] Period [d]
10.5
10.2
11
10.4
11.5
10.6
g] g]
a a
m 12 m
[0 [010.8
V V
12.5
11
13
11.2
13.5
11.4
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Phase Phase
Fig.7 Same as Fig. 5, but for GT Ori and a period P = Fig.8 Same as Fig. 5, but for IRAS 05354–0142 and a
920.32d. periodP =373.31d.
416d,consistentwithliteraturevaluesassumingareasobale areremarkable,aswellasitsabnormallyblueV −J colour
0
errorof2%,anditsharmonicatP ≈832d.Thereisalsoa foritsredJ −K andIRASfluxexcessemission.
s
spurious(systematic)peakatP =1d.Thetriangularshape
ofminimaandmaximainthephase-foldedlightcurvemay
3.2.2 Newvariablegiantcandidates
be useful for modelling the astrophysical properties of the
Mirastar. IRAS05354–0142(No.30). WithV −K =7.1±0.3mag,
T s
ithadthereddestoptical-infraredcolouramongthe∼1500
Tycho-2/2MASS stars investigated by Caballero & Solano
GTOri(No.66). Itisasemi-regularpulsatingstar,orig- (2008). According to them, “the closeness of IRAS 0534–
inally proposed to be a likely Mirastar with variations be- 0142 to the Ori I–2 globule may explain part of its red-
tween11.5and12.5magbyHoffmeister(1934).Afterwards, dening, but not all. It might be an S-type or a C-type gi-
it has been monitored by several authors (e.g. Kurochkin ant with a very late spectral type and very low effective
1949; Braune 2001). The F0 spectral type determined by temperature”. From our ASAS data, IRAS 05354–0142 is
Nesterov et al. (1995) is in contradiction with the red op- thebrighteststarinTable2(V ≈10.2–11.2mag)andhas
0
tical and near-infrared colours, the detection of GT Ori by the fourth largest power spectrum. Besides, it is one the
IRASatthe12and25µm,anditslowpropermotion,ofless four most clearly variable stars in this study, together with
than 3masa−1. The photometric and astrometric informa- XOri,RYOri,andGTOri.Thelightcurvepowerspectrum
tionandthestrongperiodogrampeakatP ∼920dandthe peaks at P = 373.31d, but there are also secondary max-
phase-foldedlightcurveinFig.7aremoreconsistentwith ima at shorter periods (Fig. 8). The multi-pattern, phase-
thesemi-regularpulsatingstatusandaprobableK-type,gi- folded light curve indicates that a harmonic study is nec-
antnatureofGTOri.Thelargeamplitudeofvariabilityof essary to disentangle the different oscillation modes of the
the star, of almost 3mag (V ≈ 10.6–13.5mag), and the giant.Atabout3arcmintothenorthliestheirregularvari-
0
overlappingofdifferent(shorter)periodsinthelightcurve ablestarV1299Ori,foundbyKaiser(1992).Itwastheonly
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10 Caballeroetal.:ThemostvariableASASstarsintheOrionBelt
1800 800
1600 700
1400
600
1200
2g] 2g]500
ma1000 ma
wer [ 800 wer [400
Po Po300
600
200
400
200 100
0 0
10−1 100 101 102 103 104 10−1 100 101 102 103 104
Period [d] Period [d]
11.5 12.5
12 13
g] 12.5 g] 13.5
a a
m m
[0 [0
V 13 V 14
13.5 14.5
14 15
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Phase Phase
Fig.9 Same as Fig. 5, but for IRAS 05285–0325 and a Fig.10 SameasFig.5,butforV1159OriandaperiodP
periodP =78.226d. =44.345d.
SIMBADobjectunidentifiedbyCaballero&Solano(2008) locus in Fig. 4 (V0 −J ∼ 4.8mag), and very low proper
in the Alnilam/Mintaka region. Tabulated coordinates are motionsmakeNo.60tobeafairgiantcandidate.
likelyincorrect.IRAS05354–0142andV1299Orimightbe
the same star, but the variability type and amplitude given
3.3 Miscellanea
by Kaiser (1992) are inconsistent with the data presented
here. In this class, we include variable objects that are neither
young stars nor background giants. Of the eight objects in
this class, only two (the dwarf nova cataclysmic variable
IRAS 05285–0325 (No. 03), IRAS 05353–0309 (No. 07),
V1159Oriandthecontactbinary2M054354–0243.6)were
IRAS05248–0037(No.54),andIRAS05312+0053(No.75).
knowntovary.Atleastthreeoftheothersixstars,including
TheyhadbeenonlyreportedbyKraemeretal.(2003)as
thenearbyearlyF-typestarHD290509,mightbeeclipsing
“infrared”sourcesandhave“highquality”fluxdensitiesat
orinteractingbinaries.
theIRAS12µm(and25µm)pass-bandsandpropermotion
absolutevaluesofafewmilliarcsecondsperyear.Ofthem,
only one had a power spectra peak larger than 500mag2 V1159Ori(No.01). Itisawell-knowndwarfnovacat-
(Table 2). The periodogram of IRAS 05285–0325 shows a aclysmic variable of ER UMa (or RZ LMi) type, which is
forest of peaks associated to the different pulsation modes a subgroup of SU UMa-type dwarf novae4 with short re-
ofthegiant.Themainmode,whichisquiteclearinFig.9, currence time of super-outburst (τ ≤ 45d). Their super-
correspondstoaperiodP =78.3±0.1d.
4 Adwarfnovaisaclosebinarystarsysteminwhichoneofthecom-
ponentsisawhitedwarf,whichaccretesmatterfromitscompanion.In
No. 60. It is reported here for the first time and has not contrasttoclassicalnovae,outburstsandsuper-outburstsindwarfnovae
result from instabilities in the accretion disc. SU UMa dwarf novae are
ameasuredIRASfluxdensity.However,itsveryredoptical
characterisedbytwodistincttypesofoutburstsintimescalesofdays(more
and near-infrared colours, which puts the star in the giant frequent)andweeks(lessfrequentandwithlargeramplitude).
(cid:13)c 0000WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.an-journal.org