|Measuring the Stellar Yields of massive stars with Herschel PACS
|The pre-supernova mass loss from massive stars can significantly enrich the ISM in nitrogen. We propose to use Herschel to determine the masses of newly synthesised nitrogen in three Wolf-Rayet (WR) ejecta nebulae. We will obtain PACS line scans of 4 IR fine structure lines for each nebula, covering the [NIII] 57um and [OIII] 88um lines, along with the density sensitive [NII] 122 and 205um lines. From these we can calculate the total ionized mass of Nitrogen along with the 57um to 88um flux ratio which will yield the N2+-O2+ abundance ratio, equal to the N-O ratio for a wide range of nebular conditions, provided the exciting stars have effective temperatures above a certain threshold value. To satisfy this constraint, we have chosen WR ejecta nebulae whose exciting stars have spectral types of WN7 or earlier, or WC7 or earlier. The total nitrogen mass can be derived from the total nitrogen flux over all the PACS IFU pixels for both N2+ and N+. This will allow the first comparisons to be drawn between derived nebular masses and stellar yield predictions for massive stars. These measurements will also allow us to quantify the N abundance enhancements for a significant sample of WR nebulae. This has not been possible before, due to (a) the high extinctions to many WR stars, which lie very close to the Galactic Plane, hindering optical spectroscopy of their nebulae; (b) the fact that optically-based nebular N-O ratios rely on line ratios of the trace ions N+ and O+, necessitating large and uncertain ionization correction factors, whereas far-IR observations sample the dominant ions, N2+ and O2+, as well as N+.
|Herschel-PACS measurements of nitrogen enrichment in nebulae around Wolf-Rayet stars . Stock D. J. et al. . Monthly Notices of the Royal Astronomical Society, Volume 441, Issue 4, p.3065-3074 . 441 . 10.1093/mnras/stu724 . 2014MNRAS.441.3065S ,
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT2_dstock_3, SPG v14.2.0. https://doi.org/10.5270/esa-ose2q56