HD 172167    HR 7001    alfa Lyra    HIP 91262
RA (2000) = 18 36 56.3364       Dec (2000) = +38 47 01.291
SpT = A0V    V = 0.03 mag    d = 7.756 pc
Proper Motion (mas/yr) = +201.03 +287.47

The Spitzer Space Telescope obtained this image of warm dust surrounding Vega. The "surprise" was the absence of clumpy structure that was seen earlier at 850 microns (Holland et al. 1998). The emission detected at 70 microns also extends much farther from the star than the 850 micron emission. At 70 microns, dust is detected as far as 70 arcseconds radius or 543 AU. At a longer wavelength, 160 microns, Spitzer images show emission as far as 105 arcseconds, or 815 AU.

Basic facts about Vega:

1) age is estimated to be between 310 Myr and 390 Myr

2) structure is a ring with inner and outer radii of 80 and 120 AU, respectively.

3) characteristic grain size is 70 microns, with characteristic temperature 80 K.

4) total dust mass estimates between 0.2-0.7 lunar mass, i.e. (1.5-5.1)x10^25 g or (7.5-26)x10^-9 M_sun

5) morphology is significantly asymmetric

6) ring is seen near face-on from our point of view. This orientation is also derived from Vega's low projected rotational velocity of 22 km/s.