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

•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 mini-SONG 20’x20’•Stellar density is not too dense nor too low

diameter ： most< 20 arcmin metallicity ： -0.8~0.2

age ： 106~1010yr

• What can we get? – Scientific goalsA: 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 curvesThe relation between spin, age and mass of starHigher 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 ：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 proto-stellar disk Prove a core accretion theory?

Lack of planet around low metallicity stars?

A. Planet frequency VS. Metallicity of host star

•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.

Lack of long period planet around low metallicity stars

B. Proto-stellar disk induced light variation

AA Tau-likeSpot-like Irregular.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?

Spot-like

AA Tau-like

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)

The problem is how to distinguish the disk

C. The spin-age-mass relation of star

Sunspot induced light variation (Meibom, et al. 2011)

Use the slowing spin rate as a clock to measure the age of a star.

By Meibom, et al. 2011

How to measure the spin of a star?

C. The spin-age-mass relation of star

• 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

By Meibom, et al. 2011

• 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 RAJ2000 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

Increa

sing a

ge

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 R band865 V<20 1195 R<20