Studying the Milky Way with pulsating stars ( 東京大学 ) Noriyuki Matsunaga (The University of Tokyo)
The first C-rich Miras found in the bulge All the AGB stars confirmed in the bulge were O-rich. C-rich Miras among OGLE-III Miras and those in Catchpole+16 Target selection based on (J-Ks) and (9-18) colors Low-resolution spectra from SAAO 74inch/SpUpNIC Boundaries for classification from Ishihara et al. (2011)
Distances to the C-rich Miras Relatively large errors remain due to the mix of interstellar and circumstellar extinction. P-W relation with J/Ks is useful to check the approximate positions. 4 Miras (and maybe another) are within the bulge. 3 foreground (including a symbiotic C-rich Mira in Miszalski+13) 4 members 1 background?
The origin of C-rich Miras It is unclear how these C-rich Miras were formed. Intermediate-age stars (around 0.5 3 Gyr)?? Old objects evolved from stellar mergers?? Accretion from a (merged) dwarf galaxy?? They are tracing a rare stellar population in the bulge. Kinematics and chemical information may help uncover their origin(s). Matsunaga et al. (2017, MNRAS, 469, 4949)
Main topics Introduction Pulsating stars as tracers of the Galactic disk New Cepheids revealing the structure of the inner Galaxy and beyond Review of new Cepheids discovered since 2011 Concluding remarks
Introduction Pulsating stars as tracers of the Galactic disk
Pulsating stars as tracers Type II Cepheid RR Lyr Classical Cepheid Mira Period-luminosity relation Distance Unique evolutionary stage Age Kinematic and Chemical information can be added with follow-up studies. Gautchy & Saio (1995)
Ks [mag] As distance indicators Period-Luminosity relations of Cepheids and Miras in the LMC (from Matsunaga et al. 2009, 2011) Classical Cepheid Mira Longer-P Miras Type II Cepheid For Miras, P-L relations are narrow only in the IR (not in the optical) log(period/day)
As age indicators Type Initial Mass Age Classical Cepheids 4 10 M 20 300 Myr Miras 1 6 M 100 Myr 10 Gyr Type II Cepheids ~1 M ~10 Gyr RR Lyrs ~1 M ~10 Gyr log (Age/yr) 8.5 300Myr 8.0 100Myr Period-Age relation of classical Cepheids (Bono et al. 2005) 7.5 7.0 30Myr 10Myr 0 1 2 log (Period/day) Miras show a loose anticorrelation between age and period (see eg. Feast et al. 2006).
Metallicity gradient of Cepheids Higher metallicity towards the inner Galaxy. Cepheids (10 300 Myr) show the most clear and tight metallicity gradient. Genovali et al. (2014, A&A, 566, 37) Genovali et al. (2015, A&A, 580, 17) [Na/Fe] [Fe/H] [Al/Fe] R GC [kpc] [Si/Fe] R GC [kpc]
MW Cepheids from classical surveys Distant Cepheids in the Galactic disk are obscured. Very important to extend the sample to a large space. Different locations along each spiral arm, a wider azimuth range, a wider range of Gactrocentric distance GC Sun The distribution of ~500 Cepheids from DDO database: overlaid on the illustration by GLIMPSE project (2008)
Cepheids waiting to be found Windmark et al. 2011, A&A, 530, A76 A simple exponential-disc model: f R, z = exp R 3.5kpc sech z z 0 20,000 Cepheids predicted (see ~2,000 new members from OGLE-IV in Udalski 2017, arxiv:1703.02980) 9,000 Cepheids may be detected by Gaia. to be detected by Gaia not to be detected by Gaia Sun GC Simulation of Cepheids to be detected by Gaia (Windmark et al. 2011)
Cepheids/Miras remain important. Many new to be found by OGLE, VVV, Gaia, LSST... No Gaia parallaxes for a large part of the disk. Cepheids and Miras are bright (especially in the IR) and can be detected across the disk. Gaia s first sky map (2016 Sep)
New Cepheids revealing the structure of the inner Galaxy and beyond Review of new Cepheids discovered since 2011
IRSF + SIRIUS 1.4-m telescope in Sutherland (SAAO) SIRIUS: FOV: about 7.7 x 7.7 Pixel Scale: 0.453 /pix, Simultaneous JHK s images. It has been steadily working for over 17 years since 2000, during which 170+ papers were published. 24+ PhD theses (20 in JP, 3 in SA) Manchester, 25 June 2004
Matsunaga et al. (2011, Nature, 477, 188) 3 Cepheids from IRSF All 3 have P~20 days, aged ~25 Myr. ~0.1 M/yr at ~25 Myr ago
Soszynski et al. (2011, AcA, 61, 275) OGLE-III survey 32 classical Cepheids (based on P-W relation, all of them seem located beyond the bulge)
5 Cepheids in the disc flare Feast et al. 2014, Nature 509, 342 Based on IRSF photometric data, Estimated distances to 5 OGLE-III Cepheids toward the bulge (Soszynski et al. 2011). The kinematics from SALT spectroscopic data are consistent with the disc rotation. The first stars ever confirmed to be in the disc flare. Other OGLE Cepheids remain to be characterized better. Cepheids identified far from the plane
Dekany et al. (2015, ApJL, 799, L12; 2015, ApJL, 812, L29) Cepheids far behind the bulge (Soszynski et al. 2012; Feast et al. 2014) 37 classical Cepheids from VVV survey
Dekany et al. (2015, ApJL, 799, L12; 2015, ApJL, 812, L29) Cepheids far behind the bulge (Soszynski et al. 2012; Feast et al. 2014) 37 classical Cepheids from VVV survey Matsunaga et al. (2016, MNRAS, 462, 414) 26 Cepheids, from IRSF, in addition to the three in the Nuclear Stellar Disk
Conflicting results in 2015/2016 Dekany et al. (2015) and Matsunaga et al. (2016) reported significantly different distributions of Cepheids in the inner part of the Galactic disk. Our work (shallower) Dekany et al. (2015) 29 classical Ceps from IRSF/SIRIUS 37 classical Ceps from VVV 11 Cepheids are common, and μ 0 (ours) are systematically larger than μ 0 (Dekany et al.). Δμ 0 ~0.5 mag
Impact of the extinction law Conversion from a color excess to an extinction depends on the extinction law, A Ks /E(H K s ). These works consider the direction of the bulge. A classical value in Cardelli et al. (1989) Label Reference Data A Ks E H K s C89 Cardelli+1989 Mixed 1.82 N06 Nishiyama+2006 IRSF 1.44 N09 Nishiyama+2009 2MASS 1.61 AG15 Alonso-Garcia+2015 VVV 1.28 M16 Majaess+2016 VVV 1.49
A(K s )/E(H-K s ) (and P-W relation) (μ 0, A Ks ) are derived with two-band magnitudes and PLRs. From the extinction law A Ks = A Ks E(H K s ) μ 0 = K s M Ks A Ks H K s (M H M Ks ) observed from PLR unknown Period-Wesenheit relations are also affected by the error in the extinction law. W HKs = K s γ (H K s ) This term doesn t work as a correction of the interstellar extinction unless γ is correct.
E H K s = 1. 5~2. 5 for our targets (the color excess can be determined regardless of the extinction law.) A K s E H K s Matsunaga et al. (2016) used the N06 coefficient. = 1. 44 A Ks = 2. 2~3. 6 A K s E H K s Dekany et al. (2015) used the N09 coefficient. = 1. 61 A Ks = 2. 4~4. 0 ~0.3 mag difference
4 Cepheids in the NSD One of the young stellar populations found in the NSD. Radial velocities also support the membership. These Cepheids are located at the distance of GC (8.0±0.5 kpc) and give a constraint on A Ks /E H-Ks. l-v diagram for Cepheids compared with CO gas and orbits around the GC 3 Cepheids within 35 pc (projected) of the GC +1 at ~50 pc Matsunaga et al. (2011) Matsunaga et al. (2015)
The λ 2 law towards Bulge The distance modulus to the GC (μ 0 =14.5±0.15 mag; Nishiyama+06b) y-axis: Apparent modulus =True modulus + Extinction Bulge red clumps split into many sub-regions give A Ks /E H-Ks =1.44 (Nishiyama+06a) x-axis: Color excess
The λ 2 law towards Bulge PLRs in H and Ks can put individual Cepheids on this diagram (without assuming the extinction law or the distance). y-axis: Apparent modulus =True modulus + Extinction 4 NSD Cepheids x-axis: Color excess
The λ 2 law towards Bulge The Nishiyama+06 law is consistent with that the 4 Cepheids are at the GC distance. y-axis: Apparent modulus =True modulus + Extinction A Ks /E H-Ks x-axis: Color excess
The λ 2 law towards Bulge A Ks /E H-Ks y-axis: Apparent modulus =True modulus + Extinction 25 other Cepheids in our survey x-axis: Color excess
The λ 2 law towards Bulge Also, we found no Cepheids on the nearer side. y-axis: Apparent modulus =True modulus + Extinction A Ks /E H-Ks x-axis: Color excess
The λ 2 law towards Bulge The extinction law of A(Ks)/E(H Ks)=1.44 is supported for the direction of the bulge. Very few Cepheids are present within ~2.5 kpc of the Galactic Centre except the NSD. Also see the discussion in the proceedings book for 22 nd Pulsation Conference at San Pedro (eds. M. Catelan & W. Gieren) y-axis: Apparent modulus =True modulus + Extinction A Ks /E H-Ks x-axis: Color excess
Classical Cepheids in the far side of the disk Cepheids far behind the bulge (Soszynski et al. 2012; Feast et al. 2014) 4 classical Cepheids in the Nuclear Stellar Disc Lack of classical Cepheids within 2.5 kpc of the GC except 4 in the Nuclear Stellar Disc ( l <2 deg) no simple exp. disc
Cepheids far behind the bulge (Soszynski et al. 2012; Feast et al. 2014) Tanioka et al. (2017, ApJ, 842, 104) 3 Cepheids from IRSF
Tanioka et al. (2017, ApJ, 842, 104) Monte-Carlo simulations allows us that two Cepheids rotate slower than the Galactic rotation (V LSR of Cepheids from Subaru/IRCS). Slow (3.1 σ) Large errors in (μ 0, A Ks ) remain by Cepheids considering far behind the the extinction bulge laws in (Soszynski Nishiyama+06 et al. 2012; and Feast Cardelli+89. et al. 2014) μ 0 =14.90 0.25 Consistent with MW rotation D (T2C) 3D extinction map (Schultheis+14) D (CC) μ 0 =13.62 0.09 Slow (1.6 σ) μ 0 =14.82 0.31
Cepheids far behind the bulge (Soszynski et al. 2012; Feast et al. 2014) New near-ir survey for the northern disk (Yanagisawa-san s talk) OGLE Cepheids (Udalski, 2017, arxiv:1703.02980) 0-10 -20-30 -40-50 -60-70
Cepheids far behind the bulge (Soszynski et al. 2012; Feast et al. 2014) KISOGP survey l=60 210 deg ~100 Cepheids OGLE VVV Gaia for the entire range (except obscured region)
KISOGP survey l=60 210 deg ~100 Cepheids Cepheids far behind the bulge (Soszynski et al. 2012; Feast et al. 2014) New surveys are discovering Cepheids (and other variable stars) spread across the Galactic disk. Spectroscopy will be important to study the disk evolution, and must be efficient for >1000 objects. OGLE VVV Gaia for the entire range (except obscured region)
Concluding remarks
Concluding remarks A large number of new pulsating stars are expected from large surveys: OGLE, VVV, Gaia, LSST Characterizing the interstellar extinction is an urgent task for mapping the wide area of disk. Gaia s proper motions will be crucial. Talk by Kawata-san and more Spectroscopic follow-up will be crucial. Kinematics and chemical abundances demanded. Near-IR spectroscopic observations are required to observe new ones in the obscured regions. Talks by Ikeda-san and Fukue-san