Resolving X-ray Sources from B-Stars - Spectroscopically Ehud Behar Department of Physics Technion Prepared for the “Other Issues” Session of the XDAP Meeting

2 Motivation Isolated late type B stars are NOT supposed to emit X-rays Nevertheless, many have been detected as (putative) X-ray sources (by Einstein, ROSAT, Chandra) This has raised the companion hypothesis, or standard stellar theory needs to be questioned Challenge for observers: Find an unseen companion –X-ray and IR Imaging (Hubrig et al. ‘01, Stelzer et al. ‘03) –WE SUGGESTED: X-RAY SPECTROSCOPY … and to identify it Interestingly, many of these targets are Chemically Peculiar stars

3 Methods Spectroscopic –UV attenuation of (He-like) forbidden lines (Gabriel & Jordan 1969) B stars are strong UV sources –Peculiar Elements Strip any element and it will emit X-rays Traditional –Astrometry –Timing –Radio, IR follow ups

4 Hunting the Hare in Leporis ( just south of Orion)

5 Choice of Target: The Case for  Lep “Isolated” B9 non-magnetic HgMn star –also known as HR 1702 & HD Nearby: 56.5 pc Detected by ROSAT (Berghöfer et al. ‘96) Companion was searched for but not found –with ~0.’’3 resolution (Hubrig et al. ‘01) XMM-Newton & Chandra/LETGS –guest observation

6  Lep Looks Coronal (RGS)

7 O VII Triplet is Normal

8 X-Ray Source Pretty Far Away from B-Star (UV Source)

9 Mn +15 The Ne-like Analog of Fe +16 Distorted wave calculations (HULLAC, Bar Shalom et al.) invaluable here for both wavelengths and relative line intensities Resonance 2p -3d line at Å

10 No Sign of Mn +15

11 The Hg Project Doron et al WARNING Do NOT Try This With an R-Matrix Code

12 Chandra Imaging

13 So, What is the Companion?  Lep-B?

14 What is  Lep-B? (cont.) Short duration flares point at magnetic activity L X = 4.4 x erg s -1 vsini (B star) < 10 km/s (Abt & Morrell ‘95) L bol = ? Age (B star): 19 Myr (Schaller et al. ‘92) In short: Fits the Orion Nebular Cluster correlations for L X with age and rotation (Feigelson et al. ’03) and not those of MS stars

15  Lep Looks Like a (relatively cold, non- accreting, record-breaking close) PMS Star HD (weak lined TTS Kastner et al. ‘04)

16 Concluding Remarks on SPECTROSCOPIC METHODS: X-ray spectroscopy can be useful for addressing astrophysical problems for which it was not considered prior to the Chandra and XMM-Newton gratings on ATOMIC CALCULATIONS: Distorted wave codes are invaluable for calculating spectra of chemically peculiar elements or generally for generating, accurate new atomic data - FAST on STELLAR PHYSICS: An increasing number of examples seem to show that late-type B stars are NOT X-ray sources … the quest for peculiar elements in the X-rays will continue elsewhere an ASTRONOMICAL APPLICATION: B stars can be used to find nearby PMS stars not easily detected by any other means on the FUTURE of this project: Follow up with Radio observation (location and spectrum) and with IR imaging (separation could be time dependent) is in progress

Questions?

Collaborators M. Leutenegger, R. Doron, M. Güdel, U. Feldman, M. Audard, S.M. Kahn