Transcript 幻灯片 1
Exoplanet Transits with mini-SONG Licai Deng @ NAOC Presented for the NJU group mini-SONG • 50cm 2 channel, with dual tube (not really needed, UVI case). • 20’x20’ FOV (limited by budget). • For SONG-north (where photometry will likely be missing (luck imaging)). • Chinese team really want to have that capability for a number of reasons, • And, more importantly, want to make good use of that capability Do what mini-SONG is really good at ! • There are tons of small telescopes out there with similar or better instruments • What makes mini-SONG unique is the SONG network and the way it schedules observations: – High duty cycle, long time baseline – Identical instruments – Can follow ToOs at any time Given all these, we should • Stay focus, and just like SONG, stare at only a few targets for the major goals • The targets should contain as many stars as possible to accommodate a variety of interests on stellar variabilities All those made us decided to go for open clusters. (need careful selection) Searching for transiting planets in open clusters with mini-SONG Hui Zhang & Ji-Lin Zhou College of Astronomy and Space Science Nanjing University • What do we prepare to do? High accuracy, continual photometry observations in a series of open clusters • Why do we choose stellar clusters? •Stellar members have almost the same age, composition and dynamic environment within a cluster. know one, know all •Stellar members are well studied within a cluster higher certainty of mass, radius, temperature and distance. •Why is the Open Cluster? • Characteristics of open cluster： statistical results of 2094 open clusters age：106~1010yr diameter：most< 20 arcmin •Very young stars： many stars with age of only million years proto-stellar disk is expected constraint on the life time of protostellar disk •Low metallicity: the least metallicity required by the formation of planet •Diameter < 20’ ,suit for the FOV of miniSONG 20’x20’ •Stellar density is not too dense nor too low metallicity：-0.8~0.2 • What can we get? – Scientific goals A: Search transiting planets in a series open clusters with varied metallicity The planet frequency as a function of the metallicity of host star B: Search proto-stellar or debris disk in a series open clusters with varied age, mass and metallicity The frequency of debris disk and its life time versus the mass, metallicity of the host star C: Detect the spin of stars by analysis their light curves The relation between spin, age and mass of star Higher certainties on the mass, radius of planets in the same cluster A. Planet frequency VS. Metallicity of host star Lack of planet around low metallicity stars? • Lack of planet around low metallicity stars ： Observation bias：It is more difficult to detect low mass planet lack of giant planet around low metallicity star lack of giant planet around young stars (low metallicity) time scale required by giant planet formation (agree with the gas accretion time scale？) Formation mechanism ：It is hard to form planet core in a low metallicity protostellar disk Prove a core accretion theory? A. Planet frequency VS. Metallicity of host star Lack of long period planet around low metallicity stars •Lack of long period planet around low metallicity stars ： Observation bias ：It is hard to detect long period planet around young stars (low metallicity and active) Formation mechanism ： Core accretion theory: Metallicity elements tends to condense at the inner part of the proto-stellar disk Gravitational instability theory: The fragmentation usually happens at the outer part of the disk. Low metallicity makes it even harder. B. Proto-stellar disk induced light variation The problem is how to distinguish the disk Spot-like AA Tau-like Spot-like AA Tau-like Irregular. The light variation patterns indicate different type of proto-stellar disks. The variation is caused by the warp of inner disk controlled by magnetic field. (Alencar et al. 2010) Number VS. Period of two type of disk in NGC2264 The peak at 3~5 days period is coincide with the peak of the hot-Jupiter, the inner boundary of disk? C. The spin-age-mass relation of star How to measure the spin of a star? By Meibom, et al. 2011 Sunspot induced light variation (Meibom, et al. 2011) Use the slowing spin rate as a clock to measure the age of a star. C. The spin-age-mass relation of star By Meibom, et al. 2011 • Light curve Spin rate of star Spin ~ age1/2 Law Age of a star • U-V photometry Color magnitude Mass of a star Spin-Age-Mass relation • Appling on other stars with planets in the same cluster planet frequency VS. age of star born time and life time of planet • On going projects： Space： • Kepler：NGC 6866, NGC 6811, NGC 6819, NGC 6791 • Corot：NGC2264 Ground： • PISCES: NGC 6791，NGC 2158, NGC 188 • STEPSS: NGC 1245 • MONITOR: ONC， NGC 2362， h & c Per ，IC 4665， NGC 2547， Blanco 1， M50 ，NGC 2516， M34 • EXPLORE-OC: NGC 2660 ， NGC 6208 • Others: M37(Hartman,et al,2007), NGC 7789(Bramich,et al.,2005), NGC 6940(Hood, et al.,2005) A few candidates are found, None of planet is confirmed! It is probably because: 1. The sample is too small. The Kepler project suggests the frequency of hot-Jupiter (and Neptune) is around 5%. However only part of stellar members of a open cluster are bright enough to perform high accuracy photometry. Need deep field observation (10% accuracy at V<20 ). 2. The continual observation is not long enough: Peak of period is around 3~5 days At least 10-days uninterrupted observation Peak at 3-5days It is probably because: 3. The dynamic environment of open cluster is not suit for planet formation. So far, no planet is found in old and high metallicity open cluster as well. If we really can not find any planet in any open cluster (very hard to believe!) A great challenge to the planet formation theory!! Our scheme • 8 open clusters are chosen (preliminary version) Varied age, suitable diameter (20’x20’), has not been observed yet • Observation schedule: 5-minutes exposal V and R band 10-15days uninterrupted observation for a single cluster 50cm aperture 300s exposal Limit magnitude vs. SNR 1” seeing Targets (preliminary) Cluster DEJ2000 Diam Dist E(B-V) Age h:m:s d:m:s arcmin pc mag [log 10 yr] IC 5146 215324 471600 20 852 0.593 6 NGC 1893 05 22 44 33 24 42 25 6000 0.45 6.48 NGC 2175 06 09 39 202912 22 1627 0.598 6.953 NGC 1931 05 31 25 341442 17 3086 0.738 7.002 NGC 6913 202357 383030 10 1148 0.744 7.111 NGC 2168 06 08 54 24 20 00 40 912 0.2 8.25 NGC 1662 04 48 27 10 56 12 20 437 0.304 8.625 NGC 6885 20 12 01 26 28 42 20 597 0.08 9.16 NGC 2682 08 51 18 11 48 00 25 908 0.059 9.409 Increasing age RAJ2000 Example: NGC 1893 Very young stellar cluster: 10^6.48 yr • total 1483 stars – VRI class 0/I/II: 1068 – VRI diskless: 415 ( 200 V<20 ) • 3-6 candidates expected! V band 865 V<20 R band 1195 R<20