1. 2009/03/18-20 East Asia VLBI Workshop 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

2. 2009/03/18-20East Asia VLBI Workshop2 Period-luminosity (PL) relation of Mira variables ► Large Magellanic Cloud (LMC) (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). Relationship in K-band (2.2μm) ► Solar-neighbourhood (Hipparcos)

3. 2009/03/18-20East Asia VLBI Workshop3 Why are the solar-neighbourhood error and scatter large? ► Large Magellanic Cloud (LMC) ► Solar-neighborhood (Hipparcos) ► Distance >> distribution ► Distance to all Miras are same ► ► Distance = distribution ► We must calculate absolute magnitude using distances. LMC

4. 2009/03/18-20East Asia VLBI Workshop4 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.

5. 2009/03/18-20East Asia VLBI Workshop5 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) Mira antenna slewing reference antenna slewing Mira 7 sec 13 sec 7 sec 13 sec 7 sec 40 sec

6. 2009/03/18-20East Asia VLBI Workshop6 Observed sources (GCVS : General Catalogue of Variable Stars)

7. 2009/03/18-20East Asia VLBI Workshop ► Parallax : 0.54 0.06 mas ► Distance : A B C D E F G A B C D E F G A B C D E F G A B C D E F G Results of UX Cygni 7 (Kurayama et al. 2005)

8. Parallax of VX UMa (Preliminary) ► Movement on the sky  Blue : Observed  Pink : Fitted ► Parallax :  0.4 0.1 mas 2009/03/18-20East Asia VLBI Workshop8

9. 2009/03/18-20East Asia VLBI Workshop9 Overlapping to Previous PL relations ► PL relation of Large Magellanic Cloud (Assuming the distance modulus of the LMC is 18.50.) VX UMa UX Cyg (Feast et al. 1989)

10. Period of VX UMa ► 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 2009/03/18-20East Asia VLBI Workshop10 (from AAVSO homepage) R I V Visual B Relative date [days] 200400 0 Mag. 4 18 8 14

11. 2009/03/18-20East Asia VLBI Workshop11 Overlapping to Previous PL relations ► PL relation of Large Magellanic Cloud (Assuming the distance modulus of the LMC is 18.50.) VX UMa UX Cyg (Feast et al. 1989)

12. Overlapping to Previous PL Relations ► Slightly above (bright) from overall results 2009/03/18-20East Asia VLBI Workshop12 UX Cyg VX UMa -6 -8 -10 2 2.8 2.6 2.4 2.2 log (period/day) Absolute mag. (Whitelock et al. 2008) Black : Hipparcos parallaxes Blue : globular cluster Red : VLBI parallaxes ► Solar-neighbourhood

13. Why Are Our Results Slightly Bright? ► 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. 2009/03/18-20East Asia VLBI Workshop13 –1 1 3 log P [days] 10 17 K (Ita et al. 2004)

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… 2009/03/18-20East Asia VLBI Workshop14

15. Thank you! 2009/03/18-20East Asia VLBI Workshop15

16. 2009/03/18-20East Asia VLBI Workshop16 50 mas