Toward the Metallicity Measurements of Microlensing Planetary Host Stars Akihiko Fukui Okayama Astrophysical Observatory (OAO), NaHonal Astronomical Observatory of Japan (NAOJ) 2016 Jan. 13 20 th Microlensing Workshop @IAP
Test for the Core AccreHon (CA) Scenario Microlensing is suitable to test the CA scenario sensihve to planets in the planetary birth place sensihve to planets around low-mass stars Past stahshcal analyses have passed a test Less massive planets are more abundant beyond the snow line Higher mass-resoluhon is required for further tests Paucity of super-neptunes? Drop at ~ Jupiter-mass around M dwarfs? => Measuring the absolute mass is important
Metallicity Dependence Stellar Metallicity is a key parameter to control planet-formahon efficiency For Jovian planets: Strong dependence on metallicity has been observed both in FGK and M dwarfs For super-earths/neptunes: No significant correlahon has been observed both in FGK and M dwarfs But, short-period planets could be affected by post-forma6on effects (e.g., migrahon, giant impacts, Hdal interachons, and stellar irradiahon) Cold planets might hold a planetary-massmetallicity correlahon if exists Occurrence rate of Jovian planet around FGK stars Kepler M-dwarf sample no-planet host super-earths Neptunes Fischer & ValenH 2005 Jovian Mann et al. 2013
A Challenge for the CA Scenario Several super-jupiters (>2Mjup) have been discovered around M-dwarfs Challenging the CA scenario Might have formed via gravitahonal instability (GI) Mass distribuhon of microlensing planets around M dwarfs All Mass constrained Metallicity could solve the issue CA requires a very high metallicity GI does not require high metallicity (e.g. Boss 2006) Fukui et al. 2015
The Most Promising Way Direct spectroscopy will be possible using the ground-based huge telescopes TMT, E-ELT, GMT Most lens stars can spahally be resolved in a few years ResoluHon of TMT/IRIS will be ~10-25 mas High light-gathering power will enable mid-resolu6on NIR spectroscopy for M-dwarf hosts TMT/IRIS can obtain R=4000 spectrum of K=22 star in 5 hours (SNR=100) (Wright+ 2014) TMT E-ELT GMT
Prospects for Spectroscopy with Current FaciliHes High-proper mohon legacy events Lens can spahally be resolved e.g., OGLE-2005-BLG-169 (K dwarf) Direct spectroscopy with a 10m-class telescope or HST might be possible OGLE-2005-BLG-169 Keck/H-band lens source Brighter lens events If the lens is much brighter than the source, lens spectra can be obtained without spahally resolving the lens e.g., OGLE-2012-BLG-0026 (G dwarf) BaHsta et al. 2015 OGLE-2012-BLG-0026 SHll challenging for M-dwarf hosts Beaulieu et al. submiked
M-dwarf Metallicity from NIR Colors Newton et al. 2014 NIR color-color diagram can be used to diagnose the metallicity of M dwarfs
OGLE-2012-BLG-0563 A high magnificahon event (A max ~600) discovered by OGLE and MOA Intensive follow-up observahons were conducted by ufun and RoboNET A clear planetary feature with q~10-3 was detected near the peak Finite source is detected, but parallax is not detected Fukui et al. 2015
AO observahons with Subaru/IRCS Date:2012 July 28 (2 months aner the event) Telescope: 8.2m Subaru Instrument: IRCS + AO Filters:J, H, and K Seeing with AO: ~0.2 The source+lens object was idenhfied in all three bands Source+Lens
Lens Brightness ExtracHon H band CTIO/H-band light curve provides apparent source flux Subtracted the apparent source flux from the source+lens flux J, Ks bands No light curves Calculated apparent source flux by es6ma6ng intrinsic source brightness and ex6nc6ons toward the source star Subtracted the apparent source flux from the source+lens flux J L = 18.33 ± 0.09 H L = 17.80 ± 0.07 K s,l = 17.69 ± 0.11
Constraint on Mass and Distance Results: M s = 0.34 +0.12-0.20 [M Sun ] D = 1.3 +0.6-0.8 [kpc] M p = 0.39 +0.14-0.23 [M Jup ] Excluded from non-detechon of parallax (123 +44-73 [M Earth ]) a (close) = 0.90 +0.52-0.50 [AU] a (wide) = 5.2 +3.1-2.9 [AU] M dwarf orbited by a cold Saturn
Colors of OGLE-2012-BLG-0563L OGLE-2012- BLG-0563L Nearby M dwarfs (Newton+ 2014) Fukui et al. 2015 Some offset, but marginally consistent with low-metallicity M dwarfs UncertainHes are too large
The Way to Improve the Color Measurements JHK-band photometric followups One limitahon was the lack of J- and K-band light curves The several calibrahon steps introduced stahshcal and systemahc uncertainhes Regularly following up in JHK-bands will be worthwhile Magnitude calibrahons are shll required MulH-epoch AO observahons in JHK by ToO Directly provide the lens colors Only a color-term correchon is required Can roughly constrain the metallicity, enough to diagnose the formahon mechanisms of super- Jupiters around M dwarfs
Summary Metallicity measurements are important to test the planetary formahon mechanisms Direct spectroscopy with ground-based huge telescopes is the most promising way One way to measure the metallicity of M-dwarf hosts with current facilihes is using NIR colors We measured the NIR colors of OGLE-2012- BLG-0563L by using Subaru telescope, resulhng in too large error bars MulH-epoch AO observahons in JHK will provide Hghter constrain on the metallicity for future events