Results 211 to 220 of about 42,848 (232)

Big, Bumpy Dust Shells Around Protoplanetary Nebulae

2001
We present evidence for parsec-sized dust shells around post-AGB objects, seen in 1SOPHOT data Furthermore, some of these data show evidence for enhanced mass-loss episodes on the timescales of thermal pulses. Preliminary studies suggest that the mass of the progenitors of these stars should be of the order of ~3M⊙.
Angela Speck, Margaret Meixner, Toshiya Ueta   +2 more
openaire   +1 more source

OH–IR sources as precursors to protoplanetary nebulae

Nature, 1990
IT has long been suspected1 that OH–IR sources, highly evolved red giant stars that have built up massive, cool gaseous envelopes through heavy mass loss, are precursors to planetary nebulae. The two kinds of object share a similar galactic distribution, and their circumstellar envelopes have comparable masses and expansion velocities2,3.
M. C. Shepherd, R. J. Cohen, M. J. Gaylard, M. E. West   +3 more
openaire   +1 more source

Formation of amorphous ice in the protoplanetary nebula

Planetary and Space Science, 1994
Abstract The criteria for formation of amorphous ice in different models of the protoplanetary nebula are developed. Assuming that comets are composed mostly of amorphous ice, it is shown that the inner boundary of formation of cometary nuclei is about 7 A.U.
Y. Mekler, M. Podolak
openaire   +1 more source

Photometric variability of five candidates for protoplanetary nebulae

Astronomy Letters, 2011
We analyze long-term UBV observations and ASAS-3 photometry for five candidates for protoplanetary nebulae—F and G supergiants with infrared excesses at highG alactic latitudes—V340 Ser, IRAS 05113+1347, V552 Pup, V448 Lac, and RV Col. These stars exhibit quasi-periodic multifrequency light variations caused by pulsations with characteristic time ...
V. P. Arkhipova, N. P. Ikonnikova, G. V. Komissarova   +2 more
openaire   +1 more source

Simple molecules and complex chemistry in a protoplanetary disk. A JWST investigation of the highly inclined disk d216-0939

Astronomy & Astrophysics
While the number of detected molecules, particularly complex organic molecules, in the solid state in astrophysical environments is still rather limited, laboratory experiments and astrochemical models predict many potential candidates.
Alexey Potapov, Hendrik Linz, J. Bouwman, W. Rocha, Johannes Martin, Sebastian Wolf, Thomas Henning, Hiroshi Terada Analytical Mineralogy Group - Institute of Germany, M. F. A. H. -. Germany, Laboratory for Astrophysics - Leiden Observatory - University Netherlands, Institute for Theoretical Physics, Astrophysics - Christian Albrecht University Kiel - Germany, N. A. O. O. Japan   +12 more
semanticscholar   +1 more source

Thermal cycling and fluctuations in the protoplanetary nebula

Icarus, 1988
Abstract The cooling of the protoplanetary nebula is controlled largely by the opacity of dust grains. Usually nebula structure models employ standard opacity tables calculated for ensembles of micron-sized dust grains, which are assumed to dominate the opacity.
G.E. Morfill, C.K. Goertz, O. Havnes
openaire   +1 more source

Probing accretion and stellar properties in the Orion Nebula with VLT/X-Shooter

Astronomy & Astrophysics
Multiple photometric studies have reported the presence of seemingly older accreting pre-main-sequence (PMS) stars in optical colour-magnitude diagrams (CMDs).
L. Piscarreta, G. Beccari, R. Claes, C. Manara, Henri Boffin, T. Jerabkova, B. Ercolano, A. Natta, S. V. van Terwisga   +8 more
semanticscholar   +1 more source

Molecular lines from protoplanetary nebulae: observations with ALMA

Astrophysics and Space Science, 2007
Planetary nebulae (PNe) are formed in a very fast process. In just about 1000 years, the nebula evolves from a spherical and slowly expanding AGB envelope to a PN, with usually axial symmetry and high axial velocities. Molecular lines are known to probe most of the nebular material in young PNe and protoplanetary nebulae (PPNe), and are therefore very ...
openaire   +1 more source

The distribution of gases in the protoplanetary nebula

Icarus, 1964
Abstract It is demonstrated that the distribution of elements in the solar system may be connected with solar magnetic fields. Relative diffusion of neutral particles and ions in a magnetic field (“ambipolar diffusion”) separates elements of different ionization potential.
openaire   +1 more source

Photometric variability of the protoplanetary nebula LSIV-12°111

Astronomy Letters, 2002
We present our photometric observations of an early B supergiant with an infrared excess, the protoplanetary object LSIV-12°111, and the previously suspected variable star NSV 24971. We confirm its photometric variability. During two observing seasons (2000–2001), the star exhibited rapid irregular light variations with amplitudes \(\Delta V \sim 0 ...
V. P. Arkhipova, N. P. Ikonnikova, R. I. Noskova, G. V. Komissarova   +3 more
openaire   +1 more source