East Asia VLBI Workshop (Seoul, 2009 Mar 18-20) Kurayama, Tomoharu (KVN/KASI) *1

1. Period-Luminosity Relation of Mira-Variables Revealed from VLBI--- Parallax Measurement Results around 500-Day Period with VLBA East Asia VLBI Workshop (Seoul, 2009 Mar 18-20) Kurayama, Tomoharu (KVN/KASI)*1 Matsui, Makoto (Kagoshima Univ.) *1 Kagoshima Univ. from 2009 April East Asia VLBI Workshop

2. Large Magellanic Cloud (LMC) Solar-neighbourhood (Hipparcos) Period-luminosity (PL) relation of Mira variables Relationship in K-band (2.2μm) (Feast et al. 1989) • The red line is the fitting result from data whose periods are less than 420 days. (van Leeuwen et al. 1997) • Error bars are caused by the uncertainties of Hipparcos’ parallax ( 1 mas). East Asia VLBI Workshop

3. Large Magellanic Cloud (LMC) Solar-neighborhood (Hipparcos) Why are the solar-neighbourhood error and scatter large? LMC • Distance >> distribution • Distance to all Miras are same • Distance = distribution • We must calculate absolute magnitude using distances. East Asia VLBI Workshop

4. Scientific target • Uncertainties in PL relation of solar-neighborhood Miras are large. • When we measure the parallaxes (that is, distances) of Miras and establish the relationship between periods and absolute luminosities, • PL relation of Miras becomes an absolute distance indicator, • we can measure the distance to the LMC, and • it is possible to measure the Galactic structure using Miras as probes. • We carried out phase-referencing VLBI observations in order to measure the parallaxes. East Asia VLBI Workshop

5. Observation • VLBA 10 stations • 22 GHz (water maser) • 5 hours 4 days • Bandwidth : 16 MHz • Velocity resolution : 0.2 km/s • Recording rate : 128 Mbps (32 Msps×2 bit×2 ch) (VLBA Home Page) 13 sec 7 sec 7 sec 7 sec 13 sec reference Mira Mira antenna slewing antenna slewing 40 sec East Asia VLBI Workshop

6. Observed sources (GCVS : General Catalogue of Variable Stars) East Asia VLBI Workshop

7. Results of UX Cygni • Parallax : 0.54 0.06 mas • Distance : A E A B C E B C D D G G F F A E A C E B B C D D G G F F East Asia VLBI Workshop (Kurayama et al. 2005)

8. Parallax of VX UMa (Preliminary) • Movement on the sky • Blue : Observed • Pink : Fitted • Parallax : • 0.4 0.1 mas East Asia VLBI Workshop

9. PL relation of Large Magellanic Cloud Overlapping to Previous PL relations VX UMa UX Cyg (Assuming the distance modulus of the LMC is 18.50.) (Feast et al. 1989) East Asia VLBI Workshop

10. Period of VX UMa 4 I 8 R Mag. V 14 Visual B 18 0 200 400 Relative date [days] (from AAVSO homepage) • In GCVS (General Catalogue of Variable Stars) : 215.2 days • Correct one • Carter 1993, J. AAVSO, 22, 69 • R band : 520 days • V band : 507 days • Uncertainty : around 10 days East Asia VLBI Workshop

11. PL relation of Large Magellanic Cloud Overlapping to Previous PL relations VX UMa UX Cyg (Assuming the distance modulus of the LMC is 18.50.) (Feast et al. 1989) East Asia VLBI Workshop

12. Overlapping to Previous PL Relations -10 • Solar-neighbourhood • Slightly above (bright) from overall results Black : Hipparcos parallaxes Blue : globular cluster Red : VLBI parallaxes VX UMa -8 Absolute mag. UX Cyg -6 2.4 2.2 2.8 2 2.6 log (period/day) (Whitelock et al. 2008) East Asia VLBI Workshop

13. Why Are Our Results Slightly Bright? 10 K 17 1 3 –1 log P [days] (Ita et al. 2004) • Physical processes of Mira variables? • Different sequence? • Hot bottom burning? • Systematical error in parallaxes? • VERA results are slightly fainter. (Nakagawa-san’s talk) • VERA also observes VX UMa. East Asia VLBI Workshop

14. Summary • Two parallaxes of Mira variables are measured with VLBA. • UX Cyg : 0.54 0.06 mas • VX UMa :0.4 0.1 mas • The period of VX UMa was wrong. • 215.5 days –> 507 – 520 days • Two Miras are plotted on period-luminosity relation. • Not so big difference • Slightly brighter than PL relation by other methods • We need confirmation works… East Asia VLBI Workshop

15. Thank you! East Asia VLBI Workshop

16. 50 mas East Asia VLBI Workshop