Download 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