Near-Infrared Spectroscopy of the Planetary Nebulae M 2–9 and AFGL 2688

Abstract

Medium-resolution 1–2.5 µm spectra of several planetary nebulae (PN) have been obtained using KSPEC, a near-infrared spectrograph designed for the University of Hawaii 2.2 m telescope. The data have been used, along with broad-band near-IR imaging, to understand the nature of the emission from these objects.The observations were performed during June 1993 on the UH 2.2m telescope using KSPEC, a new near-IR spectrograph (Hodapp et al. 1993). KSPEC is designed to cover the atmospheric windows from 1 – 2.5µm in one spectral frame on a 256×256 pixel NICMOS-3 HgCdTe detector array at the f/31 focus of the UH 2.2m telescope. The spectrograph provides medium (λ/Δλ ͂600) spectral resolution for classification work, emission line detection, and redshift measurements. The instrument uses a second NICMOS-3 array for slit-viewing. This facilitates the acquisition of optically invisible objects, documents the slit position, and aids in position control during the spectroscopic observations. The slit-viewing detector has a field-of-view of ͂1 square arcmin.A 1 × 7 arcsec slit was used to obtain spectra of the PN at several positions, including the central star, bright knots, and the ring or lobes of the nebula. Two of the PN observed were the bipolar nebulae M 2–9 and AFGL 2688. In M 2–9, the spectrum of the central source is dominated by H recombination lines and a strong continuum rising towards longer wavelengths consistent with a 795K blackbody flux. Also present are lines of He I and [Fe II]. In contrast, the N knot and E lobe show little continuum emission. The N knot spectrum consists of lines of [Fe II] and hydrogen recombination lines, and the E lobe primarily of H2 lines in the 2 – 2.5 µm region. In AFGL 2688, the main lobe consists of mainly continuum emission presumably reflected from the central star. The N lobe also has a reflected continuum component. Both the N and E lobes show strong H2 emission consistent with a thermal excitation mechanism.Key wordsM 2–9AFGL 2688Nebulae:PlanetaryInfrared: Spectra