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Parallax measurements of the Mira-type star UX Cygni with phase-referencing VLBI

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). Large Magellanic Cloud (LMC). Solar-neighbourhood (Hipparcos).

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Parallax measurements of the Mira-type star UX Cygni with phase-referencing VLBI

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  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) 8th EVN Symposium

  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). 8th EVN Symposium

  3. Large Magellanic Cloud (LMC) Solar-neighborhood (Hipparcos) Why is the solar-neighbourhood scatter large? LMC • Distance >> distribution • Distance to all Miras are same • Distance = distribution • We must calculate absolute magnitude using distances. 8th EVN Symposium

  4. 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). 8th EVN Symposium

  5. 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. 8th EVN Symposium

  6. 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 8th EVN Symposium

  7. 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 8th EVN Symposium

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

  9. Positions of all maser spots • Origins are fixed to the position of B on 2001 Feb 22 (1st obs.). A E A B C E B C D D G G VLA observation (Bowers et al. 1994) F F A E A C E B Position of star B C D D G G F F 8th EVN Symposium

  10. Fitted movements excluding linear motions and observed positions Fitting for parallax • 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 : 8th EVN Symposium

  11. Discussion 1 : Distance to LMC UX Cygni Distance : Apparent mag. : 1.96 mag Absolute mag. : Distance modulus to LMC : Distance to LMC : Typical value : 50 kpc LMC 565 days 9.33 0.19 mag (Feast et al. 1989) (Alves, 2004) 8th EVN Symposium

  12. Discussion 2 :Position and motion in the Galaxy • Position • Motion For Galactic centre Galactic centre 8.20 0.01 kpc UX Cygni The Sun UX Cygni Assuming Adopted proper motion is the average. 8th EVN Symposium

  13. Summary and future Parallaxes derived with VLBI (Published from 1986 to 2006) • 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) This result 30％ uncertainty Pulsars Stars Star formations 8th EVN Symposium

  14. Reference • Kurayama, T. et al. 2005, ApJ, 627, L49 8th EVN Symposium

  15. Large Magellanic Cloud Solar-neighborhood Discussion 1 : PL relation PL relation in K-band (2.2μm) This result This result (Assuming the distance modulus of the LMC is 18.50.) 8th EVN Symposium

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