Robertson, Jeff W.

UARK (University of Arkansas )

Journal of the Arkansas Academy of Science Volume 63 Article 31 2009 New Eclipsing Close Binary Star In The Constellation of Sextants Jeff W. Robertson Arkansas Tech University, jrobertson@atu.edu Follow this and additional works at: https://scholarworks.uark.edu/jaas  Part of the External Galaxies Commons Recommended Citation Robertson, Jeff W. (2009) "New Eclipsing Close Binary Star In The Constellation of Sextants," Journal of the Arkansas Academy of Science: Vol. 63 , Article 31. Available at: https://scholarworks.uark.edu/jaas/vol63/iss1/31 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission 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 Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. Journal of the Arkansas Academy of Science Vol. 63, 2009198New Eclipsing Close Binary Star In The Constellation of SextantsJ. W. RobertsonDepartment of Physical Sciences, Arkansas Tech University, Russellville, AR 72801Correspondence: jrobertson@atu.eduDuring a Center for Backyard Astrophysics (CBA)photometric campaign on cataclysmic variable VZ Sex,one of the field stars was serendipitously discovered tobe a variable by the author. A finding chart for thenew variable is shown in Figure 1, the new variablenoted as “var.” The coordinates of the object are(J2000) 09o45’03.75” +04o01’29.4” found by utilizingALADIN (Bonnarel et al. 2000).Figure 1: Finding chart for new variable. North is up, East is to theleft, with a FOV ~20x20 arcminutes. The new variable “var” andthe comparison stars used (comp, chk1, chk2) for photometry arelabeled in addition to the other variables in the field (VV and VZSex).The field near VZ Sex was observed on 12 nightsduring 2008 January with an 0.30-m Schmidt-Cassegrain telescope. A total of 5,919 images werecollected, unfiltered, with a thermoelectrically cooledSBIG ST-9 CCD camera and had exposure times of 30-60 seconds. All of the CCD images were processedusing Cmuniwin (http://c-munipack.sourceforge.net/).This PC-based software with a graphical user interfacewas converted from individual algorithms originallydeveloped by Filip Hroch (1998). In short, the imagesare 1) converted to FITS format if necessary, 2) flat-fielded and dark subtracted if desired, 3) processed tofind stellar targets and photometrically measuredutilizing the methods of DAOPHOT (Stetson 1987), 4)target lists are pattern matched to identify stars in eachimage via the algorithm of Groth (1986), and 5)variable, comparison and check stars selected togenerate differential photometry and light curves.Additionally, the inhomogeneous ensemble photometrymethod (Honeycutt 1992) used in the analysis of thedata with Cmuniwin can yield the light curve for everystar in the field of interest and help find variable stars.The variability of this star was revealed by the large0.26 sigma uncertainty in its instrumental ensemblemagnitude (mag) compared to other field starsaveraging 0.05 mag at the same brightness. Theuncertainty in the differential magnitude photometrywas estimated by comparing the non-variablecomparison and check stars that averaged 0.017 mag,see (C-K) on figures 2 and 4. Observations on two ofthese nights are shown as differential light curves inFigure 2 and show a close eclipsing binary star withprimary and secondary eclipses.A period search of the data using the phase-dispersion minimization (PDM) method ofStellingwerf (1978) is shown in Figure 3. A total of5000 individual frequencies were tested in the intervalfrom 0.2 to 0.6 days. The strongest peak is flanked byspurious peaks. These represent aliases of the trueperiod (P) due to observation time sampling inherent inthe data. Corresponding spurious periods () can beidentified as described by Lafler & Kinman (1965),1/ = 1/P ± nfor simple values of n. Some of these aliases areindicated as n in Figure 3. Power spectra methods asdescribed by Horne and Baliunas (1986) andSchwarzenberg-Czerny (1996) were also utilized toverify the orbital period obtained via PDM.The methods were also tested on several lightcurve data sets that were constructed such that the timeof true observations was preserved, but the observedmagnitudes were randomly shuffled and assigned tothese observation times. This has the effect ofevaluating the “windowing” function for the periodsearches, discriminating against periods inherent in thetime sampling of the data and further checking the198Journal of the Arkansas Academy of Science, Vol. 63 [2009], Art. 31Published by Arkansas Academy of Science, 2009New Eclipsing Close Binary Star in the Constellation of SextantsJournal of the Arkansas Academy of Science Vol. 63, 2009199validity of the power found in the strongest signal.These search results revealed a period of 0.27337 days.Figure 2: Light curves of the new variable star on two nights during2008 January. Variable minus Comparison (V-C) star differentialmagnitudes are in the upper panels, Comparison minus Check (C-K) non-variable stars plus an arbitrary 3 magnitude offset in thelower panels.Figure 3: Phase dispersion minimization showing the orbital periodand aliases.Times of minima were measured from the lightcurve for both primary and secondary eclipses utilizingthe method of Kwee and van Woerden (1956) andlisted in Table 1. These values were then used in ananalysis of the observed versus predicted eclipse timesfrom a simple linear ephemeris T=T0+PxN with aperiod (P) of 0.27337 days, where T0 is the time ofprimary mid-eclipse and N is the integer orbital cyclecount.The orbital light curve of the system is shown inFigure 4 using the adopted linear ephemeris foundfrom the O-C analysis for primary eclipse minimumlight,Minimum=2454467.875367(3) + 0.273378(9) × N.Table 1: Eclipse times for primary and secondary minima.Eclipse Times Cycle2454467.875523 0.02454468.970523 4.02454474.982974 26.02454475.803898 29.02454477.990228 37.02454478.810321 40.02454479.904548 44.02454480.997827 48.02454481.817233 51.02454483.731170 58.02454484.004438 59.02454486.738720 69.02454468.830931 3.52454474.846434 25.52454477.853875 36.52454478.947156 40.52454479.767204 43.52454480.859942 47.52454483.867169 58.52454485.780074 65.52454486.878207 69.5As can be seen in comparing Figures 2 and 4,significant scatter is introduced when overlayingmultiple orbits in the phased light curve. In Figure 2,the single nights reveal slightly shallower minima atsecondary eclipse than at primary eclipse.Additionally, the irregular shape of the light curve atmaximum light and their slightly unequal maxima is a199Journal of the Arkansas Academy of Science, Vol. 63 [2009], Art. 31https://scholarworks.uark.edu/jaas/vol63/iss1/31J.W. RobertsonJournal of the Arkansas Academy of Science Vol. 63, 2009200classic indicator of magnetic activity (star spots) onone or both of the stars.Figure 4: Phased orbital light curve of the new variable.Because of the continuous change in brightnessover the orbital cycle and the short orbital period, thestars are very close together in this system. Thereforeit is expected that they are in a circular orbit andsynchronously rotating, which is supported by the lightcurve morphology. This proximity will tend to makethe stars tidally distorted and create such an observedlight curve.It is likely that tidally enforced synchronousrotation of the stars in this system helps enhance theirmagnetic activity level as they are spun up by theirorbit, compared to single stars. Rotation, especiallyrapid rotation, is a prerequisite for the creation ofstrong magnetic phenomena seen in stars through aninternal dynamo. For a recent review see Donati(2004).Collection of multicolor light curve and subsequentbinary modeling will help establish parameters such asthe stellar spectral types, temperatures and sizes of thetwo stars in this newly discovered close binary system.Literature CitedBonnarel F, P Fernique, O Bienayme, D Egret, FGenova, M Louys, F Ochsenbein, M Wenger,and JG Bartlett. 2000. The ALADIN InteractiveSky Atlas. Astronomy and Astrophysics 143:33.Donati J. -F/eds. Maeder A & Eenens E. 2004. IAUSymposium No. 215; November 2002; Cancun,Mexico. 258p.Groth EJ. 1986. A pattern-matching algorithm fortwo-dimensional coordinate lists. AstronomicalJournal 91:1244.Honeycutt RK. 1992. CCD ensemble photometry onan inhomogeneous set of exposures. Publicationsof the Astronomical Society of the Pacific 104:435.Horne JH, and SL Baliunas. 1986. A prescriptionfor period analysis of unevenly sampled timeseries. Astrophysical Journal 302:757.Hroch F/eds. Dusek J & Zejda M. 1998. ComputerPrograms for CCD Photometry. Proceedings ofthe 29th Conference on Variable Star Research;November 1997; Brno, Czech Republic. 30 p.Kwee K, and H van Woerden. 1956. A method forcomputing accurately the epoch of minimum of aneclipsing variable. Bulletin of the AstronomicalInstitutes of the Netherlands XII:464.Lafler J, and TD Kinman. 1965. The calculation ofRR Lyrae periods by electronic computer.Astrophysical Journal Supplementary Series11:216.Schwarzenberg-Czerny A. 1996. Fast and statisticallyoptimal period search in uneven sampledobservations. Astrophysical Journal 460:107.Stellingwerf RF. 1978. Period determination usingphase dispersion minimization. AstrophysicalJournal 224:953.Stetson PB. 1987. DAOPHOT - A computer programfor crowded-field stellar photometry. Publicationsof the Astronomical Society of the Pacific 99:191.200Journal of the Arkansas Academy of Science, Vol. 63 [2009], Art. 31Published by Arkansas Academy of Science, 2009

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New Eclipsing Close Binary Star In The Constellation of Sextants

ScholarWorks@UARK

Journal of the Arkansas Academy of ScienceVolume 63 Article 312009New Eclipsing Close Binary Star In TheConstellation of SextantsJeff W. RobertsonArkansas Tech University, jrobertson@atu.eduFollow this and additional works at: http://scholarworks.uark.edu/jaasPart of the External Galaxies 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. (2009) "New Eclipsing Close Binary Star In The Constellation of Sextants," Journal of the Arkansas Academy ofScience: Vol. 63 , Article 31.Available at: http://scholarworks.uark.edu/jaas/vol63/iss1/31Journal of the Arkansas Academy of Science Vol. 63, 2009198New Eclipsing Close Binary Star In The Constellation of SextantsJ. W. RobertsonDepartment of Physical Sciences, Arkansas Tech University, Russellville, AR 72801Correspondence: jrobertson@atu.eduDuring a Center for Backyard Astrophysics (CBA)photometric campaign on cataclysmic variable VZ Sex,one of the field stars was serendipitously discovered tobe a variable by the author. A finding chart for thenew variable is shown in Figure 1, the new variablenoted as “var.” The coordinates of the object are(J2000) 09o45’03.75” +04o01’29.4” found by utilizingALADIN (Bonnarel et al. 2000).Figure 1: Finding chart for new variable. North is up, East is to theleft, with a FOV ~20x20 arcminutes. The new variable “var” andthe comparison stars used (comp, chk1, chk2) for photometry arelabeled in addition to the other variables in the field (VV and VZSex).The field near VZ Sex was observed on 12 nightsduring 2008 January with an 0.30-m Schmidt-Cassegrain telescope. A total of 5,919 images werecollected, unfiltered, with a thermoelectrically cooledSBIG ST-9 CCD camera and had exposure times of 30-60 seconds. All of the CCD images were processedusing Cmuniwin (http://c-munipack.sourceforge.net/).This PC-based software with a graphical user interfacewas converted from individual algorithms originallydeveloped by Filip Hroch (1998). In short, the imagesare 1) converted to FITS format if necessary, 2) flat-fielded and dark subtracted if desired, 3) processed tofind stellar targets and photometrically measuredutilizing the methods of DAOPHOT (Stetson 1987), 4)target lists are pattern matched to identify stars in eachimage via the algorithm of Groth (1986), and 5)variable, comparison and check stars selected togenerate differential photometry and light curves.Additionally, the inhomogeneous ensemble photometrymethod (Honeycutt 1992) used in the analysis of thedata with Cmuniwin can yield the light curve for everystar in the field of interest and help find variable stars.The variability of this star was revealed by the large0.26 sigma uncertainty in its instrumental ensemblemagnitude (mag) compared to other field starsaveraging 0.05 mag at the same brightness. Theuncertainty in the differential magnitude photometrywas estimated by comparing the non-variablecomparison and check stars that averaged 0.017 mag,see (C-K) on figures 2 and 4. Observations on two ofthese nights are shown as differential light curves inFigure 2 and show a close eclipsing binary star withprimary and secondary eclipses.A period search of the data using the phase-dispersion minimization (PDM) method ofStellingwerf (1978) is shown in Figure 3. A total of5000 individual frequencies were tested in the intervalfrom 0.2 to 0.6 days. The strongest peak is flanked byspurious peaks. These represent aliases of the trueperiod (P) due to observation time sampling inherent inthe data. Corresponding spurious periods () can beidentified as described by Lafler & Kinman (1965),1/ = 1/P ± nfor simple values of n. Some of these aliases areindicated as n in Figure 3. Power spectra methods asdescribed by Horne and Baliunas (1986) andSchwarzenberg-Czerny (1996) were also utilized toverify the orbital period obtained via PDM.The methods were also tested on several lightcurve data sets that were constructed such that the timeof true observations was preserved, but the observedmagnitudes were randomly shuffled and assigned tothese observation times. This has the effect ofevaluating the “windowing” function for the periodsearches, discriminating against periods inherent in thetime sampling of the data and further checking the198Journal of the Arkansas Academy of Science, Vol. 63 [2009], Art. 31Published by Arkansas Academy of Science, 2009New Eclipsing Close Binary Star in the Constellation of SextantsJournal of the Arkansas Academy of Science Vol. 63, 2009199validity of the power found in the strongest signal.These search results revealed a period of 0.27337 days.Figure 2: Light curves of the new variable star on two nights during2008 January. Variable minus Comparison (V-C) star differentialmagnitudes are in the upper panels, Comparison minus Check (C-K) non-variable stars plus an arbitrary 3 magnitude offset in thelower panels.Figure 3: Phase dispersion minimization showing the orbital periodand aliases.Times of minima were measured from the lightcurve for both primary and secondary eclipses utilizingthe method of Kwee and van Woerden (1956) andlisted in Table 1. These values were then used in ananalysis of the observed versus predicted eclipse timesfrom a simple linear ephemeris T=T0+PxN with aperiod (P) of 0.27337 days, where T0 is the time ofprimary mid-eclipse and N is the integer orbital cyclecount.The orbital light curve of the system is shown inFigure 4 using the adopted linear ephemeris foundfrom the O-C analysis for primary eclipse minimumlight,Minimum=2454467.875367(3) + 0.273378(9) × N.Table 1: Eclipse times for primary and secondary minima.Eclipse Times Cycle2454467.875523 0.02454468.970523 4.02454474.982974 26.02454475.803898 29.02454477.990228 37.02454478.810321 40.02454479.904548 44.02454480.997827 48.02454481.817233 51.02454483.731170 58.02454484.004438 59.02454486.738720 69.02454468.830931 3.52454474.846434 25.52454477.853875 36.52454478.947156 40.52454479.767204 43.52454480.859942 47.52454483.867169 58.52454485.780074 65.52454486.878207 69.5As can be seen in comparing Figures 2 and 4,significant scatter is introduced when overlayingmultiple orbits in the phased light curve. In Figure 2,the single nights reveal slightly shallower minima atsecondary eclipse than at primary eclipse.Additionally, the irregular shape of the light curve atmaximum light and their slightly unequal maxima is a199Journal of the Arkansas Academy of Science, Vol. 63 [2009], Art. 31http://scholarworks.uark.edu/jaas/vol63/iss1/31J.W. RobertsonJournal of the Arkansas Academy of Science Vol. 63, 2009200classic indicator of magnetic activity (star spots) onone or both of the stars.Figure 4: Phased orbital light curve of the new variable.Because of the continuous change in brightnessover the orbital cycle and the short orbital period, thestars are very close together in this system. Thereforeit is expected that they are in a circular orbit andsynchronously rotating, which is supported by the lightcurve morphology. This proximity will tend to makethe stars tidally distorted and create such an observedlight curve.It is likely that tidally enforced synchronousrotation of the stars in this system helps enhance theirmagnetic activity level as they are spun up by theirorbit, compared to single stars. Rotation, especiallyrapid rotation, is a prerequisite for the creation ofstrong magnetic phenomena seen in stars through aninternal dynamo. For a recent review see Donati(2004).Collection of multicolor light curve and subsequentbinary modeling will help establish parameters such asthe stellar spectral types, temperatures and sizes of thetwo stars in this newly discovered close binary system.Literature CitedBonnarel F, P Fernique, O Bienayme, D Egret, FGenova, M Louys, F Ochsenbein, M Wenger,and JG Bartlett. 2000. The ALADIN InteractiveSky Atlas. Astronomy and Astrophysics 143:33.Donati J. -F/eds. Maeder A & Eenens E. 2004. IAUSymposium No. 215; November 2002; Cancun,Mexico. 258p.Groth EJ. 1986. A pattern-matching algorithm fortwo-dimensional coordinate lists. AstronomicalJournal 91:1244.Honeycutt RK. 1992. CCD ensemble photometry onan inhomogeneous set of exposures. Publicationsof the Astronomical Society of the Pacific 104:435.Horne JH, and SL Baliunas. 1986. A prescriptionfor period analysis of unevenly sampled timeseries. Astrophysical Journal 302:757.Hroch F/eds. Dusek J & Zejda M. 1998. ComputerPrograms for CCD Photometry. Proceedings ofthe 29th Conference on Variable Star Research;November 1997; Brno, Czech Republic. 30 p.Kwee K, and H van Woerden. 1956. A method forcomputing accurately the epoch of minimum of aneclipsing variable. Bulletin of the AstronomicalInstitutes of the Netherlands XII:464.Lafler J, and TD Kinman. 1965. The calculation ofRR Lyrae periods by electronic computer.Astrophysical Journal Supplementary Series11:216.Schwarzenberg-Czerny A. 1996. Fast and statisticallyoptimal period search in uneven sampledobservations. Astrophysical Journal 460:107.Stellingwerf RF. 1978. Period determination usingphase dispersion minimization. AstrophysicalJournal 224:953.Stetson PB. 1987. DAOPHOT - A computer programfor crowded-field stellar photometry. Publicationsof the Astronomical Society of the Pacific 99:191.200Journal of the Arkansas Academy of Science, Vol. 63 [2009], Art. 31Published by Arkansas Academy of Science, 2009

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New Eclipsing Close Binary Star In The Constellation of Sextants

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