This paper presents new near-infrared observations of the planetary nebula NGC 2346. The data include a broad K-band image, an image in the H_2 vibrationally excited 1-0S(1) line and K band slit spectra at three positions in the nebula. In the H_2 1-0S(1) line, the nebula is characterized by a central, bright torus, surrounded by weaker emission with a typical butterfly shape, as seen in Hα and CO lines. The K band spectra show 11 H_2 lines with excitation energies from 6150 to 12552 K. The H_2 data have been compared to the predictions of models which follow the evolution with time of the H_2 emission in PNe of different core mass and shell properties (Natta & Hollenbach 1998). These models compute the emission originating in the photodissociation region (PDR) created at the inner edge of the neutral shell by the UV radiation of the central core, as well as the emission in the shock associated with the expansion of the shell inside the precursor red-giant wind. In NGC 2346, a PDR origin of the H_2 emission in a low-density molecular shell (n≲ 10(4) cm(-3) ) is indicated. At these low densities, time-dependent H_2 chemistry and X-ray heating of the neutral gas enhance the predicted PDR H_2 line intensity by large factors.
Vicini B, Natta A, Marconi A, Testi L, Hollenbach D, Draine B (1999). A near-infrared study of the planetary nebula NGC 2346. ASTRONOMY & ASTROPHYSICS, 342, 823-830.
A near-infrared study of the planetary nebula NGC 2346
Testi L;
1999
Abstract
This paper presents new near-infrared observations of the planetary nebula NGC 2346. The data include a broad K-band image, an image in the H_2 vibrationally excited 1-0S(1) line and K band slit spectra at three positions in the nebula. In the H_2 1-0S(1) line, the nebula is characterized by a central, bright torus, surrounded by weaker emission with a typical butterfly shape, as seen in Hα and CO lines. The K band spectra show 11 H_2 lines with excitation energies from 6150 to 12552 K. The H_2 data have been compared to the predictions of models which follow the evolution with time of the H_2 emission in PNe of different core mass and shell properties (Natta & Hollenbach 1998). These models compute the emission originating in the photodissociation region (PDR) created at the inner edge of the neutral shell by the UV radiation of the central core, as well as the emission in the shock associated with the expansion of the shell inside the precursor red-giant wind. In NGC 2346, a PDR origin of the H_2 emission in a low-density molecular shell (n≲ 10(4) cm(-3) ) is indicated. At these low densities, time-dependent H_2 chemistry and X-ray heating of the neutral gas enhance the predicted PDR H_2 line intensity by large factors.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
