arXiv:2006.04430v1 [astro-ph.SR] 8 Jun 2020 [email protected] jfl[email protected] a eietfidfo pia pcr ( spectra optical from identified stars binary be Some i involved. can point distances single the a of as because images appear usually bla Binaries tracing and candidates. distances hole measuring stars, understandi of evolution parameters, the stellar determining example, for a tla aaeessc sms,rdu,adluminosity and 1971 fundamen- radius, the mass, derive as (see to such us parameters allow stellar revealed tal They are small (EB). sight, very binaries of ing a line ( stars, the eclipsing to binary as aligned the closely all fraction, Among (SB). binaries 1905 a yang fan iaysses omni tr,pa motn oe in, roles important play stars, in common systems, Binary yee sn L using Typeset D 5 atversion raft orl akCnr o srpyis eateto Physic of Department Astrophysics, for Centre Bank Jodrell aile l 1967 al. et Daniel ; ; b ilat 2006 Willmarth & Abt isn2012 Wilson Keywords: aao.Tebnre ntectlgaemsl ihaperiod a with cut-o mostly 0.22-day are a catalog the in simula binaries Carlo The Monte a Catalog. both using by calculated is probability et,tenme fpooer n ailvlct observa velocity e radial the positi and photometry information: of contains number st catalog the binary depth, The the time. all first Among the curves. for light the on analysis Fourier felpigbnre r eonzdb e filter new a Lomb-Sc by the recognized from are derived binaries are eclipsing binaries of of identi periods to orbital constructed The is pipeline software A Telesco surveys. Spectroscopic (PTF) fiber infor Multi-Object spectroscopic Area with Sky Large binaries the eclipsing 88 of catalog a aao fSotPro pcrsoi n cisn Binar Eclipsing and Spectroscopic Period Short of Catalog A , ,2 3 2, 1, iaispa e oe ndtriigselrprmtr a parameters stellar determining in roles key play Binaries 1 ainlAtooia bevtre,CieeAaeyo S of Academy Chinese Observatories, Astronomical National ff ihr j richard unn&Ege2006 Engle & Guinan A J cietmeaueo bevbestar observable of temperature ective T une E X ,2020 9, twocolumn 1. sas)bnre icuigmlil) ls sas)b (stars:) — close multiple): (including binaries (stars:) ; sas)bnre:spectroscopic binaries: (stars:) — 3 colo srnm n pc cec,Uiest fChines of University Science, Space and Astronomy of School ra&Zitr2005 Zwitter & Prša . INTRODUCTION ; long 6 nesn1991 Andersen ff eateto srnm,BiigNra nvriy Beiji University, Normal Beijing Astronomy, of Department hc scnitn ihtelwpoaiiyo neclipsing an of probability low the with consistent is which , ,5 4, tl nAASTeX62 in style n r emdspectroscopic termed are and ) su - ushan su 4 eateto srnm,Tigu nvriy ejn 100 Beijing University, Tsinghua Astronomy, of Department ,tes-aldeclips- so-called the ), ; , isn&Devinney & Wilson ,3 1, apel&Curtis & Campbell ; 2 PC atc,K 1-,Psdn,C 12,USA 91125, CA Pasadena, 314-6, KS Caltech, IPAC, rae l 2016 al. et Prša ozhang bo , T n srnm,TeUiest fMnhse,Ofr Road, Oxford Manchester, of University The Astronomy, and s 6 e u guo rui ff n ufc rvt fosral trlog star observable of gravity surface and , ABSTRACT ng ck ). n , ine,2ADtnRa,Cayn itit ejn 100101 Beijing District, Chaoyang Road, Datun 20A ciences, ,3 1, ltTest Flat ubai yu ybnr addtsb xmnn hi ih curves. light their examining by candidates binary fy n rmr cisn antd n ie eclipsing time, and magnitude eclipsing primary on, ain aigavnaeo bevtosfo both from observations of advantage taking mation, Bsuiscnb trbtdt onGorcei 1783. in Goodricke John to attributed of beginning be The can studies thousand. EB hundred several reached now r dnie sbakhl addts(see candidates hole black as identified are wp hpe 1938 Shapley & Swope Vogel Herschel 2015 2006 2000 (M33) Galaxy Triangulum the (see and An- (M31) the Clouds, Galaxy Magellanic dromeda the to distances cand the standard determine a to as used are They tool. powerful particularly evolutio stellar for testbeds (see as theories serve systems binary Thus, rmwr yEwr 18)adwsue xlctyby explicitly used was comes and binary" (1889) "spectroscopic Edward term by The work from stars. double for inadra aafo h DSSrp 2Standard 82 Stripe SDSS the from data real and tion in,lretrda eoiydi velocity radial largest tions, fls hnoedy h eiddsrbto shows distribution period The day. one than less of r,1 iaisaeietfida cisn binaries eclipsing as identified are binaries 13 ars, , e(AOT n h aoa rnin Factory Transient Palomar the and (LAMOST) pe fe w etre fosrain,teE apehas sample EB the observations, of centuries two After cisn iaiswt pcrsoi nomto r a are information spectroscopic with binaries Eclipsing cdm fSine,Biig104,China 100049, Beijing Sciences, of Academy e 1 e dnie rmteLMS T Surveys PTF & LAMOST the from Identified ies ecasf h cisn iaisb applying by binaries eclipsing the classify We . depoigselreouinmdl.W build We models. evolution stellar exploring nd hnribai zhongrui rl ehd h e itnusigfeatures distinguishing key The method. argle g107,Pol’ eulco China of Republic People’s 100875, ng .Sm B ihbt pia n -a observations ; X-ray and optical both with EBs Some ). ; aznk aslv1997 Sasselov & Paczynski unne l 1998 al. et Guinan aae ta.2014 al. et Casares ( nre:elpig—(tr: iais general binaries: (stars:) — eclipsing inaries: 1890 ( 1802 .A euto utpersac activities(e.g., research multiple of result a As ). hbire l 2007 al. et Chabrier , a h rtt s h em"iaystar" "binary term the use to first the was ) 1 8,China 084, kai iayrttn ihsc period. a such with rotating binary - igcui ming ; ; ). ewra1943 Ferwerda yte&Wlo 2001 Wilson & Wyithe , ,3 1, ff g ogwang song rne iaytype, binary erence, h false-positive The . ; ; ors&Rbs2002 Ribas & Torres acetrM39L UK 9PL, M13 Manchester aznk Pojmanski & Paczynski , ; 1 China , ad 1946 Baade n ji and i ta.2013 al. et Liu - ; egliu feng oao tal. et Bonanos ,the ), ). ,3 1, le n , 2 Yang et al. size of the EB sample increased to several thousand. In the and the catalog are presented in section 3. In section 4, we past twenty years, due to the results from photometric mi- assess our catalog and discuss the 0.22 day cut-off in the or- crolensing surveys (e.g., EROS, Grison et al. 1995; MA- bital period distribution. In section 5, we give a summary. CHO, Alcock, et al. 1997; OGLE, Udalski, et al. 1998, 2. THE DATA USED FROM LAMOST AND PTF Wyrzykowskiet al. 2004; NSVS, Otero et al. 2004), the sam- ple size grew rapidly to about 15,000. Paczynski´ et al. (2006) The catalog is established from the survey products of then almost doubled the number by identifying and classify- LAMOST and PTF. We use LAMOST to derive stellar pa- ing 11,076 eclipsing binaries from the All Sky Automated rameters and the radial velocity of the observable star. PTF Survey (ASAS). The work from Paczynski´ et al. (2006) is data is used to obtain the orbital period and morphological particularly important because of their use of Fourier trans- features of the light curve. form in analyzing light curves. In this work, our analysis 2.1. LAMOST Data uses the same Fourier technique. Kepler space mission iden- LAMOST (Large Sky Area Multi-Object fiber Spectro- tified 2165 EBs with precise light curves (Prša et al. 2011; scopic Telescope) employs the Guo Shou Jing Telescope Matijevicˇ et al. 2012). Soszynski´ et al. (2016) published a which is a 4 meter aperture Schmidt telescope with a 20 list of over 450,000 eclipsing binary candidates toward the square degree field of view. Taking 4000 spectra per ex- Galactic bulge in OGLE survey. posure, the limiting magnitude is r = 17.8 at resolution R EB catalogs with spectroscopic information are chal- ∼ 1800 (see overview: Zhao et al. 2012; Cui et al. 2012). lenging to produce since the multiple spectroscopic ob- The survey contains two parts: the LAMOST Extra Galac- servations required are highly time-consuming activities. tic Survey (LEGAS) and the LAMOST Experiment for The first large sample of spectroscopic binaries was made Galactic Understanding and Exploration (LEGUE) survey by Campbell & Curtis (1905). The ninth edition of this (Deng et al. 2012). sample was published in (Pourbaix et al. 2004), extending Spectroscopic binaries can be classified if the spectral lines the number of spectroscopic binaries to 2386. Catalogs from both companions are visible (a double-lined spectro- of solar-type spectroscopic stars (e.g., Abt & Levy 1975; scopic binary) or if the spectral lines from only one star Duquennoy & Mayor 1991; Raghavan et al. 2010) increased are detectable (a single-lined spectroscopic binary) (e.g., the total number of spectroscopic binaries by a few hundred. Matijevicˇ et al. 2010, 2011). The identification of double- Among all the binary star observations, the EBs with spec- lined spectroscopic binaries in LAMOST spectra is generally troscopic information, providing the most comprehensive difficult due to limited spectral resolution (R∼ 1800, equiva- constraints on the binary parameters, are still rare. lent to ∼150 km s−1) unless the radial velocities or the spec- This paper describes a catalog of spectroscopic and eclips- tral types of the component stars are significantly different ing binaries from the Large Sky Area Multi-Observationfiber (for example, white dwarf-main sequence binaries, Ren et al. Spectroscopic Telescope (LAMOST) survey and the Palomar 2014). The forthcoming LAMOST-II medium-resolution Transient Factory (PTF) data. The combination of a very spectroscopic survey (MRS, Zhang et al. 2019) with resolu- large number of spectra and photometry light curves enables tion increased to R∼ 7500 will assist in identification. Work us to systematically study binary systems (Gao et al. 2014; is in progress on searching for single-lined and double-lined Kao et al. 2016). Spectra tell us more about the observable spectroscopic binaries by modeling spectra (Zhang et al. in stars, while the light curves are used to determine the or- prep.). In this research, we identify binary stars via eclipsing bital properties of the transit system. We utilize "Flat Test" and significant radial velocity differencesof the same compo- method on the light curves to remove contamination by vari- nent in multi epoch observations. All the systems identified able stars such as Cepheid and RR Lyrae stars. are regarded as single-lined spectroscopic binaries. Our catalog contains 88 spectroscopic and eclipsing bina- Xiang et al. (2017) released the fourth edition of the value- ries, among which 13 EBs are newly identified. The sources added catalog of the LAMOST Spectroscopic Survey of the in the catalog all have good quality light curves. The catalog Galactic Anticenter (LSS-GAC DR4). LSS-GAC is a major contains orbital parameters, as well as the stellar parameters part of the LEGUE project. The catalog contains more than of the observable companion. Some parameters like effective 3 million stars down to a limiting magnitude of r ∼ 17.8 mag, temperature of observable star Teff, surface gravity of observ- centered on the Galactic anticentre (|b|≤ 30◦, 150 ≤ l ≤ 210◦). able star log g help to constrain the evolution of binary stars. The stellar parameters are derived by a pipeline based on The binaries in the catalog show the 0.22 day cut-off in pe- minimum chi-square template matching (LSP3; Xiang et al. riod distribution which supports the rareness of binary stars 2015). The radial velocity (RV, center shifts of the spectra rotating with such a period. lines) and stellar atmospheric parameters (effective tempera- The paper is organized as follows. In section 2, we briefly ture T , surface gravity log g, metallicity) are the free pa- describe the survey data. The binaries selection algorithm eff rameters of the template fitting. 3
We chose sources with multi-epoch observations in LSS- GAC DR4, requiring ∆RVmax (the difference between the highest and smallest RV values of the same component of 106 a given target) to be 2 times larger than the largest radial ve- locity error. The typical spectral signal-to-noise ratio (SNR) −1 is > 10. The radial velocity precision is about a few km s 105 (Xiang et al. 2017). This procedure helped us select 128,833 Numbers objects with 421,436 observations. The number of observa- tions are shown in Figure 1. Those large RV variation stars 104 could be binary systems, or variable stars such as RR Lyrae, 0 2 4 6 8 10 etc. We then cross matched these candidates with the PTF Distance (arcsec) data. 0.7
0.6 106 0.5
105 0.4
104 0.3 MagStd 0.2 103 0.1 102 Number ofstarsNumber 0.0 14 16 18 20 101 Mag
100 0 10 20 30 40 Figure 2. PTF Astrometry and Photometry precision. Upper panel: Number of observations the astrometry precision. The x-axis is the position difference for the same source between SDSS and PTF. The y-axis is the matched Figure 1. The number of observations of LAMOST targets. number at certain position difference. Lower panel: the photome- try precision. The x-axis is magnitude while the y-axis is the mag standard deviation. The red line indicates the median value of the 2.2. PTF Data magnitude error. The Palomar Transient Factory (PTF) employs an 8 square degree camera installed on the 48 inch Samuel Oschin tele- The sources selected from the LAMOST data were scope. A 60-inch telescope is used for following-up observa- matched to the PTF light curve data base1. 39,179 stars with tions. The survey aims at time-domain events with cadences 2,784,673 observation frames, requiring the goodflag=1, ′ from 90 seconds to a few days (Law et al. 2009; Rau et al. were retrieved both in g and R band. The tag "goodflag" 2009). With exposure time of 60 seconds, the PTF 5σ limit- ensures the quality of the photometry in PTF. We analyzed ing magnitude is mg′ ∼ 21.3 and mR ∼ 20.6. The PTF collab- these sources in our binary systems identification pipeline. oration released more than 8 billion light curve tables prior 3. THE CATALOG OF SPECTROSCOPIC AND to Sep.1 2016. ECLIPSING BINARIES To select a radius for cross-matching, we randomly chose 100,000 non-variable stars in the SDSS stripe 82 Standard 3.1. Finding Binaries Catalog (Ivezic´ et al. 2007). The position difference between Our method of finding binaries is built into our software SDSS and PTF is used to validate the PTF astrometry preci- pipeline and involves two steps. The first is the Lomb- sion (see Figure 2). The sharp decrease in cross-match radius Scargle periodogram (Lomb 1976; VanderPlas & Ivezic´ occurs at 2 arcsecs. Considering the uncertainty of LAMOST 2015; VanderPlas et al. 2012) which searches for the orbital astrometry, we took 3 arcsecs to be the cross-match radius period. The second is the Flat Test developed by us which between the PTF and LAMOST data. removes artifacts as well as contamination from other vari- 5 We also randomly chose 10 sources in the SDSS Stripe able stars. In addition, every light curve is subject to a visual 82 Standard Catalog to evaluate the photometry precision of inspection to assure the purity of the sample. PTF multi-epoch observations. We used the magnitude stan- We applied the Lomb-Scargle periodogram for PTF data dard deviation of the standard stars as the statistical error of to search for significant periods. The significant period is PTF photometry (see Figure 2). The magnitude standard de- viation is less than 0.1 in the magnitude range 14 to 20 which is the magnitude range for our work. 1 https://irsa.ipac.caltech.edu/cgi-bin/Gator/nph-dd 4 Yang et al.
1.0 1.0
0.8 0.8 0.25 0.6 0.6
0.20 0.4 0.4 0.2 0.2 Lomb-Scargle Power Lomb-Scargle Power Lomb-Scargle 0.0 0.0 0.15 0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 period (days) period (days) 1.0 14.2 0.10 0.8 14.4
Lomb-Scargle Power Lomb-Scargle 0.6 0.05
Mag 14.6 0.4
0.2 14.8 0.00 Power Lomb-Scargle 0 50 100 150 200 250 300 0.0 period (days) 0.0 0.5 1.0 1.5 2.0 0.0 0.2 0.4 0.6 0.8 1.0 period (days) phase
0.25 Figure 4. The period finding process, using LPSEB2 as an example. The upper left-hand panel has the largest bin size. The upper right 0.20 panel has the bin size reduced by a factor of 10 and the lower-left by a further factor 10. The lower right panel shows the light curve 0.15 folded with the optimized period. The upper left panel has the same bin size as used in Figures 7 and 10. The red dashed line indicates 0.10 the optimized period which is half of the orbital period. The inten- Lomb-ScarglePower 0.05 sity of the real peak is weak in the upper left panel. Reducing the bin sizes reshapes the peak intensity with the real peak becoming 0.00 stronger and surrounded by a clump of peaks. The final reduction 0.0 0.5 1.0 1.5 2.0 2.5 3.0 period (days) in bin size in the lower-left panel does not significantly change the intensity distribution. Figure 3. The period power distribution. Upper: power distribution of all the periods. Lower: power distribution of the period from 0 to 3 day. The vertical lines show the period gathering at 1 day, and the most evident power is within 0.05 day of 1 day. We found harmonic periods at 0.25 and 0.5 day. a long timescale power excess (in Figure 3), which was due to the difficulty with long-time calibration. We accept only identified as the period at peak intensity if the peak is higher orbital periods between 0.01 to 10 day. After following these than a level predicted by false positive probability. The peak procedures, we were left with 275 variable sources with si- here we applied is an optimized peak using the method from nusoidal periods. VanderPlas et al. (2012). The optimization is a two-step grid These variable sources were then analyzed using the Flat peak searching. First, it searches a broad grid for some can- Test method we have developed which is a filter for investi- didates and then zooms in using a narrower grid to find the gating the characteristics of a light curve. For the close binary best estimation of the period peak. This method avoids pos- eclipsing systems we were interested in, the systems should sible false peak detections due to binning. The real peak is be highly orbitally circularized (Hurley et al. 2002). In most sometimes smoothed to be smaller when the binning size is cases, the binary systems have a shorter phase at eclipse than too large. A solitary peak is treated as improbable if a clump out of eclipse. Outliers appear among a few overcontact sys- of peaks appears when reducing the binning size. The period tems like some RR Centauri (Yang et al. 2005), which might finding process is illustrated in Figure 4. be missed by our detection. Over an orbit, tangential velocity The false positive probability we applied contains two can be taken as a sinusoidal function over time. Radial ve- parts. The first is the false alarm probability reported by locity which is orthogonal to the tangential velocity is more Lomb (1976). We required the evidence level of 99.99%. commonly used since it can be calculated from the spectra The second is based on the statistical properties of the peri- of the binary. A typical light curve and the associated radial odogram. The threshold is defined as the 3σ excess to the velocity curve are shown in Figure 5. median value of the power spectral density. The period must The light curves of eclipsing binaries should be flatter at simultaneously satisfy both parts of the false probability to the top than at the bottom, which enables them to be distin- be accepted as a significant period. guished from the RRc Lyrae variable stars(Kallrath, & Milone Then we put all the sources’ periodogramstogether (in Fig- 2009). RRc Lyrae stars sometimes have a symmetrical, si- ure 3) to remove artifact signals. The orbital periods signifi- nusoidal light curve, unlike Cepheid and RRa, RRb Lyrae. cantly cluster at 1 day and its harmonic periods such as 0.25 Moreover, the RR Lyrae stars have a typical radial velocity or 0.5 day, because of the alternation between night and day amplitude of about 30km/sto 50km/s, which locates at a sim- for the ground-based telescope. We rejected sources if the ilar place as EBs in the RV distribution. The Flat Test helps 5