This is the first real astronomy project I ever worked on, in 2000-2001.

The purpose of this project is to find out the angular expansion of the planetary nebula BD+30^{o}3639, by comparing the two-epoch Hubble Space Telescope (HST) images, and combining with the HST STIS spectroscopy to find the distance of the nebula.

Above is the HST image of BD+30^{o}3639 in Hα waveband (wavelength 656 nm), taken on Nov. 4, 1999. Planetary nebulae are the general end state of the evolution of low mass stars. The distance of planetary nebula is hard to measure, because many generally used methods to measure the distances of stars fail for planetary nebula. BD+30 is a special planetary nebula, in its young age, rapid evolution, and chemical inhomogeneity.

We measured the expansion of BD+30, from its two-epoch images taken on Mar. 6, 1994, and Nov. 4, 1999, respectively, by several methods. Shown above is the measurements of angular expansion based on the shifts of individual diffusing knots. Solid bars show the result from Hα images, and dashed bars are for [NII] images.

Together with the spectra from HST STIS observation in [CII] band, we constructed a 3-D model for this nebula, as show above.

Finally, the distance of BD+30 was measured to be 1.94+/-0.33 kpc. This result was then refined combined with other observation results and computations. A better distance estimate turned out to be about 1.2 kpc, which indicated a much smaller and compact central star. This work was published in Astronomical Journal in 2002. And this is certainly one of my favorite first-authored papers!

Li, Jianyang, Harrington, J.P., Borkowski, K.J., 2002. The angular expansion and distance of the planetary nebula BD30°3639. Astronomical Journal 123, 2,676-2,688. arXiv: 0202170.