Robertson, Jeff W.

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 59 Article 312005New Pulsating Variable Discovered in theConstellation AndromedaJeff W. RobertsonArkansas Tech University, jeff.robertson@atu.eduFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the Stars, Interstellar Medium and the Galaxy CommonsThis article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able toread, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking priorpermission from the publisher or the author.This General Note is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the ArkansasAcademy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu.Recommended CitationRobertson, Jeff W. (2005) "New Pulsating Variable Discovered in the Constellation Andromeda," Journal of the Arkansas Academy ofScience: Vol. 59 , Article 31.Available at: http://scholarworks.uark.edu/jaas/vol59/iss1/31210New Pulsating Variable Discovered In The Constellation AndromedaJeff W. RobertsonArkansas Tech University, Department ofPhysical Sciences, 1701 N.Boulder, Russellville, AR 72801-2222Correspondent: jeff.robertson@atu.eduA new pulsating variable star, HH95 HV And-7, is found near the cataclysmic variable HV And, which is a part of theIndiana University RoboScope observing program (Honeycutt and Turner, 1992). A finding chart generated with Aladinsoftware (Bonnarel et.al, 2000) is shown in Fig. 1. Its coordinates are (J2000) 00°40'46.23" +43°23'57.9". This star was initiallycalibrated as a secondary photometric standard star with V=15.277 and B-V=0.281 for the field of HV And (Henden &Honeycutt, 1995), but it suspiciously had the largest standard deviation of the group of standards (dv = 0.14). Its variabilitydetailed here means that it can not be used as a photometric standard.RoboScope is an 0.41-m telescope fully automated forunattended differential CCD photometry of cataclysmicvariables and related objects located in the Morgan-Monroestate forest north of Bloomington Indiana. Ituses a liquidnitrogen cooled, thinned SITe CCD with 24 micron pixelsin an array of size 512_512 pixels yielding a 14x14 arcminutefield of view and typically obtains 1-2 exposures per clearnight for ~150 objects. The field of HV And was observedon 318 separate nights from HJD 2448473 (UTD 1991-08-04) through HJD 2450141 (UTD 1996-02-27) through astandard Johnson V filter. The inhomogeneous ensemblephotometry (Honeycutt, 1992) used on the RoboScopedatabase can yield the light curve for every star in the fieldof interest. The variability was revealed by the large 0.14sigma uncertainty in its instrumental ensemble magnitudeshown in Fig. 2.A period search of the RoboScope data for this starusing the method of Home and Baliunas (1986) is shown inFig. 3. A total of 5000 individual frequencies were testedfrom 0.1 to 2.0 days. The strongest peak at 0.4661 day isflanked by spurious peaks at 0.32, 0.87, 0.34, 0.53 days.These represent aliases of the true period (P) due to thetime sampling frequency (/) of the data (~1 day). Theycorrespond to spurious periods (P) found from1/P = 1/P ± e/t(Lafler &Kinman, 1965) for values of e =+1, -1, +1/2,and -1/4 respectively. Power spectra were also generated forseveral data sets constructed such that the time of trueobservations was preserved, but the magnitudes wererandomly shuffled and assigned to these times. This has theeffect of evaluating the "windowing" function for the periodsearch, discriminating against periods associated with thetime sampling of the data and further checking the validityof the power found in the strongest peak. No peaks withpower larger than ~5 were found compared to ~ 120 for thetrue period.The search results reveal a pulsating variable with aperiod of 0.46614(5) days as shown inthe phased light curvefor integer cycle (N) in Fig. 4 using the ephemerisMaximum = 2448400.0(0) + 0.46614(5) _N.The accuracy in the period was estimated byminimizing the total distance (string-length) between phaseddata points for various periods near the peak period. Sincethe observational data is over a timescale much larger thana single period, the folding of the data in phase allows theperiod to be obtained to high accuracy since differentperiods would cause larger string-lengths in the phased lightcurve. The taxonomy of its light curve, namely the 0.5magnitude amplitude, the ~1/2 day period and symmetricsinusoidal shape is indicative an RR Lyrae pulsatingvariable, most likely RRc (Feast, 1996).Since itis not associated witha known globular cluster,it is likely a galactic halo object or old, thick disk member ofour galaxy (Feast, 1999). Using its mean magnitude ofmv=15.3 and a simple Period-Luminosity relationship forRR Lyrae stars MV= -2.8 log P - 0.6 (Eggen, 1994), yieldsan absolute magnitude of MV = 0.328 and a distance of-10,000 parsecs (=32,600 Ly).Acknowledgments.- Igratefully acknowledge the ever-changing vanguard of RoboScope "baby-sitters" who keepthe RoboScope system operational and always include KentHoneycutt, Brice Adams, George Turner, andBillKopp.Journal of the Arkansas Academy of Science, Vol. 59, 2005210Journal of the Arkansas Academy of Science, Vol. 59 [2005], Art. 31Published by Arkansas Academy of Science, 2005211Jeff W. Robertson• • ••.•• •.• • ¦¦ *...• HVAncf*tm• *• •. variable • .? •. •'¦•:• v-¦. J£ -. ....• . ¦ . #•chart for the new variable, HH9.5 HVAnd-7, near the cataclysmicFig. 1. A14x14 arcminute findingEast is to the left in the figure.HV And. North is up andFig. 2. Standard deviation of ensemble magnitudes for nearby stars in the field revealing variability.Journal of the Arkansas Academy of Science, Vol. 59, 2005211Journal of the Arkansas Academy of Science, Vol. 59 [2005], Art. 31http://scholarworks.uark.edu/jaas/vol59/iss1/31212New Pulsating Variable Discovered InThe Constellation AndromedaFig. 3. Differential ensemble photometry ofHH95 HV And-7.120 i ., ,—p . 1 . , . . . . 1 . 1 1 n; LBD ¦¦¦¦¦|| | ¦ ¦ ¦ J ;100- L0D '--¦ -: . 00 r-:»- lm \ \\ :1I-"r:* : 20 : : :A '¦ II_l IIII1I-1^1—J I-I-J \—H-—»X.-il-AM-D.-l* 0.4S5 0.47 0.4"S >.4J|-P«rod (d*y«l "m0 0.& 1 15 SPertod rd&jc)Fig. 4. Apower spectrum period search of the light curve data in Fig. 3.Journal of the Arkansas Academy of Science, Vol.59, 2005212Journal of the Arkansas Academy of Science, Vol. 59 [2005], Art. 31Published by Arkansas Academy of Science, 2005213Jeff W. Robertson15 I 1 1 1 1 1 1 1 r- 1 1 i i ~~i'II, Field Variable in Andromeda I lliIJil4 tHH95lHV AncJ-7 \ i*911nl! -Iff % '- jjfk, it; |#k-¦ ty UH» t/ ? ri '17-15.6 I ' '' ' ' ' ' ' ' ' ' ' ' ' '0 0.5 1 1.5-i>132H->rHdQ£d•^cJ>Phase (2448400.0 -f 0,466145*N;Fig. 4. A power spectrum period search of the light curve data in Fig. 3.Literature CitedBonnarel, F., P. Fernique, O. Bienayme, D. Egret, F.Genova, M.Loiiys, F. Ochsenbein, M. Wenger, andJ.G. Bartlett 2000. The ALADINInteractive Sky Atlas.Astronomy and Astrophysics 143:33.Eggen, O J. 1994. Photometry of F-K type bright giants andsupergiants. Astronomical Journal 107:2131.Feast, MW. 1999. Cepheids as distance indicators.Publications of the Astronomical Society of the Pacific111:775.Feast, MW. 1996. Light Curves of Variable Stars, A PictorialAtlas (C. Sterken. and C. Jaschek, eds.), CambridgeUniversity Press.Henden, AA,RKHoneycutt 1995. Secondary photometricstandards for northern nova-like cataclysmic variables.Publications of the Astronomical Society of the Pacific107:324.Honeycutt, R K. 1992. CCD ensemble photometry on aninhomogeneous set of exposures. Publications of theAstronomical Society of the Pacific 104:435.Honeycutt, R K, GW Turner. 1992. Robotic telescopes inthe 1990's (A. V.Filippenko, ed.) Astronomical Society ofthe Pacific Conference Series 34:77.Home, J H, SL Baliunas. 198b". A prescription for periodanalysis of unevenly sampled time series. AstrophysicalJournal 302:757.Lafler, J and TD Kinman. 1965. The Calculation of RRLyrae Periods by Electronic Computer. AstrophysicalJournal Supplementary Series 11:216.Journal of the Arkansas Academy of Science, Vol. 59, 2005213Journal of the Arkansas Academy of Science, Vol. 59 [2005], Art. 31http://scholarworks.uark.edu/jaas/vol59/iss1/31

New Pulsating Variable Discovered in the Constellation Andromeda

Abstract

Similar works

Full text

Available Versions

ScholarWorks@UARK