Stellar variability monitoring in open clusters with mini-SONG X.B. Zhang National Astronomical Observatories, Chinese Academy of Sciences

contents Mini-SONG Overview Main Science goals Interesting subjects concerned Predicted results

Mini-SONG Overview A global photometry system; Shares the sites and operation net-work with the North SONG.

Instruments & parameters: Double-tube 50 cm reflector; F/9.5 equatorial mount; 2k×2k CCD; SDSS or Johnson filters

Capability & utilities: FOV: 20’×20’ ; image scale of 0.6”/pixel; Photometry precision: mag for V=15 and 0.011mag for V=16 ( 1 single exposure); 0.003, mag for V=15, 16 respectively (10 exposures combined). Time-resolution: 1 min.; Duty-cycle: > 40%; Two-color simultaneously.

Main Science goals Multi-color photometric survey of open clusters; To obtain the unique multi-color CMDs of about 300 nearby open clusters and determine the basic parameters by isochrone fitting, by single site. Stellar variability monitoring in open clusters; Long-term, time-series photometry on about selected clusters, each with a time span longer than 1 month. Follow-up photometry of ToOs such as GRB, SN etc.

Why open clusters? More effective for denser stars; The same evolution history and environment of member stars; Definite parameters known from other ways;

The probable mini-SONG OC targets 337 OCs collected as the initial candidates, each with the modest coordinates, distance modulus (brightness) and diameters ( /webda.html), /webda.html

Interesting subjects concerned Eclipsing binaries Basic data: fraction & distributions in mass ratio, orbital period etc.; Test the theory of stellar evolution; Effects of mass transfer and angular momentum loss, constraints to the model of binary evolution.

Example. 1 V12 in NGC188, a detached binary discovered by Zhang et al. (2002, 2004) Zhang, et al., 2002, 2004 Meibom et al., 2009

Zhang, Deng & Lu, 2009 Example. 2 TX Cnc, a W UMa star In the praesepe cluster

Pulsating stars: Detect and compile the complete sample of several types of pulsating stars, SPB,  Cephei,  Scuti etc.; Blue & red edges of the instability stripe for each types of variables based on large-sample study. Comparison asteroseismic study with known physical parameters.

Example  Scuti variables in NGC6811 Luo & Zhang et al., 2009

Example. 4: 18 SPBs in NGC7654 Luo, Zhang & Han, 2011

Transit searching for Jupiter-like planets; Detailed by Prof. Zhou Stellar eruptive events. CVs, flares of late-type stars

Predicted results Unique, high-precision CMDs and basic physical parameters will be determined for about 300 nearby open clusters,; Light variability of tens of thousands of stars be monitored by continuous, long-term photometry, a discovery of hundreds to thousands of variables in various types is expected; Transits and some other unexpected events

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