1. A Survey of Orion A with XMM and Spitzer: SOXS
Scott Wolk
Harvard-Smithsonian
Center for Astrophysics
In collaboration with: Tom Megeath, Lori Allen, John Bally, Luisa Rebull
Marc Gange, Guisi Micela, Salvo Sciortino, Lee Hartman, Fred Walter,
John Stuaffer, Joanna Olivaria and Rob Gutermuth

2. Goals for the SOXS
Multi-wavelength observations are providing a wealth of information on the distribution and motions of stars, protostars, and cores in giant molecular clouds.
These data are an essential constraint on models of the formation and evolution of clusters.
Identify the PMS stars without disks - A full cluster census.
Study the relative importance of clustered and isolated star formation.
Examine the effect of environment on star formation and disk evolution.
Study Transition disk timescales
Effect of X-rays, especially flares on planet forming disks.

3. Orion A
CO/Optical map from CfA mm group

4. Orion A Orion B 105 M molecular cloud Orion Nebula
One of the nearest regions of clustered star formation
One of the most active regions of distributed (i.e. isolated) star formation within 500 pc.
Orion Nebula
Orion A
13CO 2.6 mm Bally et al.

5. Orion A 105 M molecular cloud
One of the nearest regions of clustered star formation.
One of the most active regions of distributed (i.e. isolated) star formation within 500 pc.

6. The Spitzer Survey of Orion A
The Spitzer survey shows that the Orion Nebula Cluster is the most concentrated region of star formation in the cloud.
Spitzer found ~1000 young low mass stars with disks and protostars in the ONC.

7. The Spitzer Survey of Orion A
In addition, the survey finds 700 young stars and 140 protostars south of the ONC.
These young stars are found in much different environment than that found in the ONC; either in small clusters of stars or in relative isolation.
These stars have formed in environments without the strong UV radiation and dense clustering found in the
ONC.
A significant fraction of the stars are in a distributed component parsecs away from the massive OB stars.
Megeath et al. in prep.

8. The Spitzer Survey of Orion A
White contours: AV = 3 (Orion)
Dots: young stars with IR-excess
Colors other than green indicate clusters of more than 10.
Nearest neighbor density
Density = 10/p r2
r =distance to
9th nearest neighbor
distributed
clustered
Megeath et al. in prep.
There is no clear border between clustered and distributed stars
Embedded clusters are not isolated, well defined objects

10. By the Numbers 1161 X-ray sources in the 9 fields
Nearly 100,000 IRAC sources in those fields.
About 140 Class I Sources in those fields
About 550 Class II sources are in the 9 fields.
About 220 (~45%) of the Class II sources were detected by XMM.
Of the 1161 X-ray sources, 882 have counterparts in the Spitzer Survey.

11. Contamination by Background X-ray Sources

12. Filtering the Contaminants

13. Colors of X-ray Sources

14. L1641 S L1641S, the DL Ori group and the HBC 498 cluster
R,G,B= 24,5.8, 3.6 m

15. L1641 S

16. L1641 N

17. Stellar Content of Orion A
Class
0/I II
III
total
X-Ray Sources
<10
220
~780
Spitzer
Sources
140
550
This is the total for the 9 fields.
It should be revised upward:
Minor incompleteness of IRAC.
Some incompleteness in cloud coverage in current XMM survey.

18. Caveats Need to really work field by field
Need to account for contamination from Orion 1A
Should be small
Examine influence of Ori.

19. Status Survey Completed March 2008
Of the 1161 X-ray sources, 882 have counterparts in the Spitzer Survey.
About 563 have IRAC colors consistent with Class III sources
99 have colors consistent with agn
221 have colors consistent with CII.
The total number of stars in the 9 fields of Orion A is about 2100.
The Class III sources appear more dispersed than the Class II sources.

21. Why Bother Looking at Young Stars in X-rays?
Young stars are X-ray bright
HMS- High energy wind shocks?
LMS- Despite pedestrian 5000K, temperatures they have hot corona.
Insight into the interior workings of LMS.
To identify young stars.
After stars lose their disks X-ray surveys are the only way to find young stellar objects
This has allowed us to understand the history of star formation in the galaxy.
Direct observation of material accreting onto very young stars.
X-rays are probably responsible for rapid heating of protoplanetary disks.

22. COUP study of the ONC 850 ks 13 papers in the APJSupp
465 refereed citations
6 Refereed Papers since
XEST - 11 paper A&A special edition on Taurus SFR.
So aren’t we done?

23. Orion A OB stars Orion B 105 M molecular cloud Orion Nebula
One of the nearest regions of clustered star formation
One of the most active regions of distributed (i.e. isolated) star formation within 500 pc.
Orion Nebula
Orion A
13CO 2.6 mm Bally et al.

24. The Spitzer Survey of Orion A
The Spitzer survey shows that the Orion Nebula Cluster is the most concentrated region of star formation in the cloud.
Spitzer 1000 young low mass stars with disks and protostars in the ONC.
L1641 N
V 380
L1641 C
HBC 498
L1641 S

25. OB STARS