nai

Project Progress

High-energy photons in the young stellar environment are known to be important in stimulating chemical reactions of molecules and producing pre-biotic materials that might later be incorporated into comets. Observational tests are sorely needed to assess the significance of such processing for Astrobiology, and to guide development of theoretical models for chemical evolution in proto-planetary environments. In this reporting period, we approached this problem from two directions: study of the mechanism and history of X-ray emission from young intermediate-mass stars, and study of hot plasma in a massive star-forming region with thousands of low-mass young stars.

We teamed with GCA member Carol Grady in the GSFC Exoplanets Laboratory to study X-ray activity of young intermediate-mass stars using the Chandra and HST observatories. We used a sub-pixel resolution technique to spatially resolve X-ray emission from two intermediate mass stars (HD 100453 and HD 169142) and their companions with 1.1 and 9.2” (arc-second) separations respectively, (Figure 1 , ). Both primary stars had significantly cooler plasma temperatures (kT ~ 0.3 keV) than either their companions or typical low-mass young stars, suggesting that the emission comes from the primary stars or from unresolved young brown dwarfs orbiting the primary stars. The X-ray luminosities are on the t-2 evolutionary track (Figure 2), which is slower than the decay of the magnetic dynamo proposed for young A-type stars. We also systematically analyzed X-ray emission from pre-main-sequence intermediate-mass stars (Herbig Ae/Be stars) using Chandra data.

{{ 1 }}

{{ 2 }}

We also studied extended hot plasma emission from the massive star-forming Carina nebula and M17, where numerous low- and intermediate-mass stars as well as very massive stars such as Eta Carinae are forming. Using the Suzaku and XMM-Newton X-ray data of this field, we found spatial variations in the extended emission , (Figure 3). Our spectral analysis revealed a deficit of iron around the star-forming core of the Carina nebula suggesting that the diffuse emission may be supernova remnants, while diffuse plasma in M17 had elemental abundance similar to solar questioning a supernova origin. Such a variation in elemental abundances would affect the formation and X-ray activity of young stars.

{{ 3 }}

We observed the comet 73P/SW3 with the Suzaku satellite and obtained a spectrum with the best energy resolution from a comet so far (Figure 4). The spectrum can be explained with charge exchange of atoms with solar wind particles, whose process may have been very important during the phase of planet formation when the solar wind was much stronger than today.

{{ 4 }}

To further study evolution of X-ray activity in young intermediate-mass stars, we again teamed with Carol Grady and won observing time of the young intermediate mass star MWC 480. We also took part in a Chandra Very Large Observing Proposal to map the Carina nebula, thereby to understand the structure of the diffuse emission and X-ray activity of young stars in the field.

References

1. “The Disk and Environment of a Young Vega Analog: HD 169142” 2007, Grady et al. Ap. J. 665:1391.

2. Collins et al. (in preparation, 2007)

3. “On the origin of the X-ray emission from Herbig Ae/Be stars” 2006, Stelzer et al. Astron. and Astrophys. 457:223.

4. “Suzaku Observation of Diffuse X-Ray Emission from the Carina Nebula” 2007, Hamaguchi et al. Pub. Astron. Soc. Japan 59:151.

5. “Suzaku Spectroscopic Study of the Extended X-Ray Emission in M1” 2007, Hyodo et al. Pub. Astron. Soc. Japan (accepted ).

6. Porter et al. (in preparation, 2007).

Talks

“Diffuse X-ray Emission from the Carina Nebula Observed with Suzaku”, K. Hamaguchi, R. Petre, H. Matsumoto, M. Tsujimoto, S. S. Holt, Y. Ezoe, H. Ozawa, Y. Tsuboi, Y. Soong, S. Kitamoto, A. Sekiguchi, M. Kokubun, Conf. on The Extreme Universe in the Suzaku Era, (2006 December 4-8, Kyoto, Japan)

Lectures

“X-ray activity on Young Stars”, K. Hamaguchi, 2006 December 13, ISAS/JAXA (Kanagawa, Japan)

“X-ray activity on Young Stars”, K. Hamaguchi, 2007 April 4, Kobe University (Kobe, Japan)

“X-ray Variations of Eta Carinae through the 2003 X-ray Minimum”, K. Hamaguchi, M. F. Corcoran, T. Gull, K. E. Nielsen, G.V. Kober, K. Ishibashi, J. M. Pittard, D. J. Hillier, A. Damineli, K. Davidson, 2007 April 23, Rochester Institute of Technology (Rochester, NY)