1. 2006.09.25-29 8th EVN Symposium 1 Parallax measurements of the Mira-type star UX Cygni with phase-referencing VLBI 8th European VLBI Network Symposium (Toruń, Poland, 2006 Sep 26-29) Tomoharu Kurayama (National Astronomical Observatory of Japan)

2. 2006.09.25-298th EVN Symposium2 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. 2006.09.25-298th EVN Symposium3 Why is the solar-neighbourhood 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. 2006.09.25-298th EVN Symposium4 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)

5. 2006.09.25-298th EVN Symposium5 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.

6. 2006.09.25-298th EVN Symposium6 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

7. 2006.09.25-298th EVN Symposium7 Observed sources ► Mira variable : UX Cygni  (α,δ)=(20h55m05.4s, +30 24 ’ 53 ’’ )  (l,b)=(74.34, -9.41)  K-band magnitude : 1.96 mag (Feast & Whitelock 2000)  Variation period : 565 days (GCVS)  Total flux density : 24.83 Jy (Comoretto et al. 1990) ► Reference source for phase-referencing : J2050+3127  Redshift : 3.18 (Fey et al. 2001) ► Separation angle of 2 sources : 1.38 ► Observed date : 2001 Feb 22, 2001 Oct 12, 2001 Nov 11, 2002 Feb 04 2001 Nov 11, 2002 Feb 04

8. 2006.09.25-298th EVN Symposium8 2001 Feb 22 2001 Oct 13 2001 Nov 11 2002 Feb 04 20 mas ► Radial velocity : -2.5 km/s ► The centres of all maps are same against the reference source. Water masers around UX Cygni -20 -10 0 10 20 [km/s] 0.4 mas 0.8 mas 175° ► Synthesized beam

9. 2006.09.25-298th EVN Symposium9 Positions of all maser spots ► Origins are fixed to the position of B on 2001 Feb 22 (1 st obs.). VLA observation (Bowers et al. 1994) Position of star 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

10. 2006.09.25-298th EVN Symposium10 Fitting for parallax ► Fitted movements excluding linear motions and observed positions ► Least square fitting with the common parallax and the linear motion of each maser spot.  Total number of parameters : 29  Total number of coordinate data : 54 ► Parallax : 0.54 0.06 mas ► Disatnce :

11. 2006.09.25-298th EVN Symposium11 Discussion 1 : Distance to LMC (Feast et al. 1989) 565 days 9.33 0.19 mag LMC UX Cygni Distance : Apparent mag. : 1.96 mag Absolute mag. : Distance modulus to LMC : Distance to LMC : Typical value : 50 kpc (Alves, 2004)

12. 2006.09.25-298th EVN Symposium12 Discussion 2 : Position and motion in the Galaxy ► Position Galactic centre UX Cygni 8.20 0.01 kpc The Sun For Galactic centre UX Cygni ► Motion Assuming Adopted proper motion is the average.

13. 2006.09.25-298th EVN Symposium13 Summary and future ► We carried out the water maser observation around the Mira-star UX Cygni with phase-referencing VLBI.  Parallax : 0.54 0.06 mas  Distance : ► This is the first parallax from water maser. ► We would like to observe more Mira variables with VERA in the future. (some sources have been already observed) 30 ％ uncertainty Parallaxes derived with VLBI (Published from 1986 to 2006) This result Pulsars Stars Star formations

14. 2006.09.25-298th EVN Symposium14 Reference ► Kurayama, T. et al. 2005, ApJ, 627, L49

15. 2006.09.25-298th EVN Symposium15 Discussion 1 : PL relation ► Large Magellanic Cloud ► Solar-neighborhood PL relation in K-band (2.2μm) This result (Assuming the distance modulus of the LMC is 18.50.)