2000 image (Kalas & Jewitt)              discovery image 1984 (Smith & Terrile)

Beta Pictoris at 0.5 micron

HD 39060    HR 2020    GJ 219.0    HIP 27321
RA (2000) = 05 47 17.1       Dec (2000) = -51 03 59.5
SpT = A5V    V = 3.86 mag    d = 19.3 pc

Proper motion (mas/yr) = +4.65 +81.96
Effective Temperature = 8200 K, Mass = 1.75 Msun, Luminosity = 8.7 Lsun
Absolute Magnitude = 2.42, Absolute Bolometric Magnitude = 2.43
Chemical abundances: X=0.70, Y=0.28, Z=0.02 (i.e. solar, X=H,Y=He,Z=heavy elements)
Age > 8 Myr

The bright star beta Pictoris is visible in the Southern Hemisphere and has the brightest, most extended dust disk of any nearby star. Optical images (0.5 microns) show the disk because dust reflects light from the central star and towards the observer.

Data from the IRAS satellite in 1983 first revealed that the star is emitting more thermal radiation at far-infrared wavelengths than is normal for this type of star. Brad Smith and Rich Terrile then obtained an optical image of what appears to be a needle-like reflection nebulosity around the star (shown above). This image was a cornerstone for the paradigm that nearby stars which emit  more far-infrared radiation than can be explained by the star alone are surrounded by circumstellar dust disks.   Many more images were subsequently obtained by several research groups.

On the left (above) we show beta Pic observed from Mauna Kea on 12 October, 1993, with University of Hawaii 2.2 meter telescope. Light from the star is blocked by a 6.5" diameter opaque spot inserted at the focal plane of the telescope, revealing the much fainter dust disk. A closer inspection of this image reveals that the northeast extension is not a mirror image of the southwest extension. The northeast extension is brighter, longer, and thinner than the southwest extension. Here we see the northeast extension extending out to 48" (790 AU) from the star, whereas the southwest extension can be traced only out to 40" (650 AU).  A gravitational perturbation, such as from a planet or a passing star, may be responsible for the asymmetries.

Below we show optical images of beta Pic obtained more recently by the Hubble Space Telescope (HST). Due to HST's excellent resolution, the images revealed that the midplane of the disk is vertically warped very close to the star, at radius 50 AU.

 In summary, optical images of beta Pic provide the following information:

1)  Disk is big:   greater than 1300 AU in radius.
2)  Dust is depleted within 100 AU of the star
3)  Grains are large-sized (10 microns)
4)  Morphology is asymmetric, possibly due to gravitational perturbation

In addition, optical spectra have revealed possible cometary activity near the star.

Basic facts about the beta Pic disk:

1) age is estimated to be between 10 Myr and 100 Myr

2) Some circumstellar hydrogen gas detected, optically thin dust disk

3) extended between 30 AU and 1300 AU radius, and possibly even farther

4) central dust depletion inward of 100 AU

5) mass in millimeter-sized grains is approximately equivalent to a few Moons

6) silicate feature detected in the mid-infrared, matching that of comet P/Halley

7) morphology is significantly asymmetric, possibly due to a planet or other companion

8) spectra of star show variable and transient absorption features, almost always redshifted, thought to arise from families of comets crashing into the photosphere every day.

9) optical color of disk is neutral, indicating that largish (10 micron) grains are dominant

10) disk is seen almost exacly edge-on from our point of view.

Burrows, C.J., Krist, J.E., Stapelfeldt, K.R., et al.  1995, "HST observations of the Beta Pictoris circumstellar disk", BAAS, vol. 27, pg. 1329
Heap, S.R., Lindler, D.J., Woodgate, B. et al. 1997, Hubble/STIS Coronographic Imagery of beta Pictoris, BAAS, vol 191, pg. 4702
Kalas, P. & Jewitt , D.  1995, "Asymmetries in the Beta Pictoris Dust Disk," Astronomical Journal, vol. 110, pg. 794.
Smith B.A. & Terrile, R. J., 1984, A circumstellar disk around Beta Pictoris, Science,  vol. 226, pg. 1421-1424.

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