Pushing the limits: detecting H<SUB>2</SUB> emission from faint bipolar planetary nebulae in the IPHAS sample

DOI: 
10.1093/mnras/stx1519
Publication date: 
01/09/2017
Main author: 
Ramos-Larios, G.
IAA authors: 
Guerrero, M. A.
Authors: 
Ramos-Larios, G.;Guerrero, M. A.;Sabin, L.;Santamaría, E.
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Volume: 
470
Pages: 
3707-3719
Abstract: 

We have obtained deep narrowband images in the near-infrared H<SUB>2</SUB> λ2.122 μm emission line for a sample of 15 faint Isaac Newton Telescope Photometric H α Survey (IPHAS) bipolar planetary nebulae (PNe) to search for molecular material. H<SUB>2</SUB> emission is found in most of them (14 out of 15), mostly associated with rings at their equatorial regions and with their bipolar lobes. These detections add to the high occurrence of H<SUB>2</SUB> emission among bipolar PNe reported in previous works, resulting from the large reservoir of molecular material in these sources and the suitable excitation conditions for H<SUB>2</SUB> emission. The correlation between detailed bipolar morphology and H<SUB>2</SUB> luminosity is also confirmed: bipolar PNe with broad equatorial rings (R-BPNe) have almost no continuum emission, are H<SUB>2</SUB> brighter and have larger H<SUB>2</SUB>/Br γ line ratio than bipolar PNe with pinched equatorial waists (W-BPNe). The origin of this dichotomy is unclear. The larger size and age of R-BPNe are consistent with shock excitation of H<SUB>2</SUB>, whereas ultraviolet pumping is most likely the excitation mechanism in the smaller and younger W-BPNe, which would explain their lower H<SUB>2</SUB> luminosity. Although both types of bipolar PNe seem to proceed from the same progenitor population, this does not imply that R-BPNe descend from W-BPNe. Otherwise, we note that some of the H<SUB>2</SUB>-weak bipolar PNe harbor post-common envelope binary systems and symbiotic stars. Finally, we suggest that the long-living H<SUB>2</SUB> emission from R-BPNe arises from a discrete distribution of compact knots embedded within the ionized gas at the equatorial region.

Database: 
ADS
SCOPUS
URL: 
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85037146711&doi=10.1093%2fmnras%2fstx1519&partnerID=40&md5=da815cdec6b96d261954f671a0598db4
ADS Bibcode: 
2017MNRAS.470.3707R
Keywords: 
ISM: lines and bands;ISM: molecules;planetary nebulae: general;infrared: ISM;Astrophysics - Solar and Stellar Astrophysics;Astrophysics - Astrophysics of Galaxies