Searching for Be Stars in the Open Clusters with PTF/iPTF. I. Cluster Sample and Be Star Candidates

We conducted a search for Be star candidates in open clusters using Hα imaging photometry of the Palomar Transient Factory Survey to investigate some connections among Be star phenomena, cluster environments, and ages. Stellar members of clusters were identified by spatial distributions, near-infrared magnitudes and colors, and by proper motions. Among 104 open clusters, we identified 96 Be star candidates in 32 clusters; 11 of our candidates have been reported in previous studies. We found that the clusters with age 7.5 < log(t(year)) ⩽ 8.5 tend to have more Be star candidates; there is about a 40% occurrence rate within this age bin. The clusters in this age bin also tend to have a higher Be fraction N(Be)/N(Be+B-type). These results suggest that the environments of young and intermediate clusters are favorable to the formation of Be phenomena. Spatial distribution of Be star candidates with different ages implies that they do not form preferentially in the central regions. Furthermore, we showed that the mid-infrared (MIR) colors of the Be star candidates are similar to known Be stars, which could be caused by free–free emission or bound-free emission. Some Be star candidates might have no circumstellar dust according to their MIR colors. Finally, among 96 Be candidates, we discovered that one Be star candidate FSR 0904-1 exhibits long-term variability on the timescale of ~2000 days with an amplitude of 0.2–0.3 mag, indicating a long timescale of disk evolution.

[1]  J. Brinkmann,et al.  HIGH-RESOLUTION H-BAND SPECTROSCOPY OF Be STARS WITH SDSS-III/APOGEE. I. NEW Be STARS, LINE IDENTIFICATIONS, AND LINE PROFILES , 2014, 1409.4668.

[2]  J. Percy,et al.  Autocorrelation Analysis of Hipparcos Photometry of Short‐Period Be Stars , 2002 .

[3]  D. Allen.  Near Infra-Red Magnitudes of 248 Early-Type Emission-Line Stars and Related Objects , 1973 .

[4]  A. Subramaniam,et al.  Optical spectroscopy of Classical Be stars in open clusters , 2011, 1108.5850.

[5]  W. P. Chen,et al.  Morphology of Galactic Open Clusters , 2004, astro-ph/0408021.

[6]  T. A. Saurin,et al.  Isolating the pre-main sequence in Collinder 34, NGC 3293, NGC 3766 and NGC 6231 , 2015, 1502.00373.

[7]  S. Bloemen,et al.  Signatures of internal rotation discovered in the Kepler data of five slowly pulsating B stars , 2016, 1611.06955.

[8]  P. Teutsch,et al.  New galactic open cluster candidates from DSS and 2MASS imagery , 2005 .

[9]  Elena Schilbach,et al.  Tidal radii and masses of open clusters , 2008 .

[10]  R. Grijs,et al.  Mass Segregation in Very Young Open Clusters: A Case Study of NGC 2244 and NGC 6530 , 2007, 0706.2723.

[11]  Shrinivas R. Kulkarni,et al.  The intermediate Palomar Transient Factory (iPTF) begins , 2013 .

[12]  Ernest E. Croner,et al.  The Palomar Transient Factory: System Overview, Performance, and First Results , 2009, 0906.5350.

[13]  P. Škoda,et al.  The Hα stellar and interstellar emission in the open cluster NGC 6910 , 2007, 0706.3709.

[14]  Yong Zhang,et al.  Discovery of new low-excitation planetary nebulae , 2014, 1402.2369.

[15]  P. Kroupa,et al.  How can young massive clusters reach their present-day sizes? , 2015, 1510.04293.

[16]  D. Leisawitz.  Physical Properties of the Molecular Clouds Found in a CO Survey of Regions Around 34 Open Clusters , 1989 .

[17]  S. Chojnowski,et al.  High-resolution H-band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability , 2017 .

[18]  Wenjin Huang,et al.  VARIABILITY OF Be STARS IN SOUTHERN OPEN CLUSTERS , 2009, 0905.0640.

[19]  J. Bjorkman,et al.  DYNAMICAL EVOLUTION OF VISCOUS DISKS AROUND Be STARS. I. PHOTOMETRY , 2012, 1207.2612.

[20]  G. Rieke,et al.  The interstellar extinction law from 1 to 13 microns. , 1985 .

[21]  S. Littlefair,et al.  Mass segregation in the young open cluster NGC 2547 , 2003, astro-ph/0308320.

[22]  B. Ou-Yang,et al.  PHYSICAL PROPERTIES OF THE B AND Be STAR POPULATIONS OF h AND χ PERSEI , 2012, 1209.5771.

[23]  N. Mowlavi,et al.  Period–luminosity relations of fast-rotating B-type stars in the young open cluster NGC 3766 , 2017, 1702.02306.

[24]  S. Dong,et al.  LAMOST OBSERVATIONS IN THE KEPLER FIELD. ANALYSIS OF THE STELLAR PARAMETERS MEASURED WITH LASP BASED ON LOW-RESOLUTION SPECTRA , 2016, 1607.01453.

[25]  E. Schilbach,et al.  THE PPMXL CATALOG OF POSITIONS AND PROPER MOTIONS ON THE ICRS. COMBINING USNO-B1.0 AND THE TWO MICRON ALL SKY SURVEY (2MASS) , 2010, 1003.5852.

[26]  Dietrich Baade,et al.  Non-radially pulsating Be stars , 2003 .

[27]  Garching,et al.  The age of the oldest Open Clusters , 2003, astro-ph/0310363.

[28]  THE EVOLUTIONARY STATUS OF Be STARS: RESULTS FROM A PHOTOMETRIC STUDY OF SOUTHERN OPEN CLUSTERS , 2005, astro-ph/0505032.

[29]  B. Sabogal,et al.  Search for Southern Galactic Be Star Candidates , 2014 .

[30]  University of Wisconsin,et al.  The Role of Evolutionary Age and Metallicity in the Formation of Classical Be Circumstellar Disks. II. Assessing the Evolutionary Nature of Candidate Disk Systems , 2007, 0708.0651.

[31]  A photometric study of the two poorly known northern open clusters NGC 133 and NGC 1348 , 2002, astro-ph/0203156.

[32]  T. C. Caetano,et al.  Proper motions of the optically visible open clusters based on the UCAC4 catalog , 2014 .

[33]  E. Feigelson,et al.  A Chandra Study of the Rosette Star-forming Complex. I. The Stellar Population and Structure of the Young Open Cluster NGC 2244 , 2007, 0711.2024.

[34]  S. Roser,et al.  Global survey of star clusters in the Milky Way - I. The pipeline and fundamental parameters in the second quadrant , 2012, 1207.4001.

[35]  A. Tarasov,et al.  Relative content of Be stars in young open star clusters , 2012 .

[36]  A Study of Be Stars in Clusters , 1976 .

[37]  John D. Monnier,et al.  GAS DISTRIBUTION, KINEMATICS, AND EXCITATION STRUCTURE IN THE DISKS AROUND THE CLASSICAL Be STARS β CANIS MINORIS AND ζ TAURI , 2011, 1109.3447.

[38]  A. Subramaniam,et al.  Be phenomenon in open clusters: results from a survey of emission-line stars in young open clusters , 2008, 0804.1498.

[39]  D. Steeghs,et al.  A deep catalogue of classical Be stars in the direction of the Perseus Arm: spectral types and interstellar reddenings , 2014, 1410.1533.

[40]  J. Wisniewski,et al.  The Role of Evolutionary Age and Metallicity in the Formation of Classical Be Circumstellar Disks. I. New Candidate Be Stars in the LMC, SMC, and Milky Way , 2006, astro-ph/0606525.

[41]  H. T. Yang,et al.  2MASS observations of Be stars , 2005 .

[42]  A. Subramaniam,et al.  NIR properties of Be stars in star clusters in the Magellanic Clouds , 2017 .

[43]  U. Cambridge,et al.  Mass segregation in young compact star clusters in the Large Magellanic Cloud — II. Mass functions , 2001, astro-ph/0111312.

[44]  D. Mcnally.  The distribution of angular momentum among main sequence stars , 1965 .

[45]  W. Gieren,et al.  On Be star candidates and possible blue pre-main sequence objects in the Small Magellanic Cloud ? , 2002, astro-ph/0204390.

[46]  N. V. Kharchenko,et al.  Global survey of star clusters in the Milky Way II. The catalogue of basic parameters , 2013, 1308.5822.

[47]  E. Paunzen,et al.  An empirical temperature calibration for the $\Delta a$ photometric system - I. The B-type stars , 2005, astro-ph/0509049.

[48]  X. Jiang,et al.  Time series photometry to search for B type variables in the young open clusters NGC 1893 and NGC 2175 , 2008 .

[49]  V. A. Marsakov,et al.  Two populations of open star clusters in the Galaxy , 2012, 1212.1560.

[50]  Keivan G. Stassun,et al.  Photometric Variability of the Be Star Population , 2016, 1609.08449.

[51]  D. Froebrich,et al.  Properties of Star Clusters - I: Automatic Distance and Extinction Estimates , 2013, 1309.0708.

[52]  R. T. Zavala,et al.  Multitechnique testing of the viscous decretion disk model - I. The stable and tenuous disk of the late-type Be star β CMi , 2015, 1510.01229.

[53]  Jiang Liu,et al.  A new approach to the infrared photometric study of Be stars , 2016 .

[54]  I. Bonnell,et al.  Mass segregation in young stellar clusters , 1998 .

[55]  A. Taylor,et al.  Near-ir observations of 101 Be stars , 1991 .

[56]  NGC 1912 and NGC 1907: A close encounter between open clusters? , 2002, astro-ph/0205100.

[57]  L. Girardi,et al.  Theoretical isochrones in several photometric systems I. Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Washington, and ESO Imaging Survey filter sets , 2002, astro-ph/0205080.

[58]  M. Bessell,et al.  JHKLM PHOTOMETRY: STANDARD SYSTEMS, PASSBANDS, AND INTRINSIC COLORS , 1988 .

[59]  W. P. Chen,et al.  Disintegration of the Aged Open Cluster Berkeley 17 , 2016, 1611.05593.

[60]  J. Porter,et al.  Classical Be Stars , 2003, 1310.3962.

[61]  Russia.,et al.  Proper motions and CCD-photometry of stars in the region of the open cluster NGC 1513 , 2002, astro-ph/0212255.

[62]  E. V. Glushkova,et al.  Automated search for star clusters in large multiband surveys: II. Discovery and investigation of open clusters in the galactic plane , 2010 .

[63]  H. Saio,et al.  Viscous excretion discs around Be stars , 1991 .

[64]  D. Baade,et al.  Cyclic variability of the circumstellar disk of the Be star $\zeta$ Tauri - II. Testing the 2D global disk oscillation model , 2009, 0901.1098.

[65]  R. Poleski,et al.  Variability of massive stars with known spectral types in the Small Magellanic Cloud using 8 years of OGLE-III data , 2013, 1310.5701.

[66]  S. Udry,et al.  Red giants in open clusters - XIV. Mean radial velocities for 1309 stars and 166 open clusters , 2008 .

[67]  E. Mamajek,et al.  INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS , 2013, 1307.2657.

[68]  Martin G. Cohen,et al.  THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE): MISSION DESCRIPTION AND INITIAL ON-ORBIT PERFORMANCE , 2010, 1008.0031.

[69]  D. Baade,et al.  Short-term variability and mass loss in Be stars II. Physical taxonomy of photometric variability observed by the Kepler spacecraft , 2016, 1608.02872.

[70]  Mark J. Pecaut,et al.  A REVISED AGE FOR UPPER SCORPIUS AND THE STAR FORMATION HISTORY AMONG THE F-TYPE MEMBERS OF THE SCORPIUS–CENTAURUS OB ASSOCIATION , 2011, 1112.1695.

[71]  I. Steele,et al.  A representative sample of Be stars V: H{\alpha} variability , 2013 .

[72]  W. P. Chen,et al.  SEARCHING FOR Be STARS IN THE OPEN CLUSTER NGC 663 , 2014, 1411.5496.

[73]  E. Ofek,et al.  Be STARS IN THE OPEN CLUSTER NGC 6830 , 2016, 1604.02276.

[74]  Be-star rotation: how close to critical? , 2003, astro-ph/0312113.

[75]  A. Code,et al.  Studies in Galactic STRUCTURE.II.LUMINOSITY Classification for 1270 Blue Giant Stars. , 1955 .

[76]  A. Moitinho,et al.  New catalogue of optically visible open clusters and candidates , 2002, astro-ph/0203351.