Related papers: Do All Low-Mass Stars Undergo Extra Mixing Process…
We used the VLA to search for 3He+ emission from two Galactic planetary nebulae (PNe): NGC6572 and J320}. Standard stellar models predict that the 3He/H abundance ratios for PNe should be 1-2 orders of magnitude higher than the primordial…
To understand the chemical evolution of the Galaxy, we need to understand the contribution of PNe in the 3He abundance. 3He abundances have been detected only in a couple of PNe, their abundances are consistent with the standard models, in…
The discrepancy between the observed abundances of 3He in the ISM and those predicted by stellar and galactic chemical evolution remains largely unexplained. In this paper, we attempt to shed some light on this unsolved problem by…
Recent observations of 3He/H in different environments tend to prove that 3He is not produced in low mass stars, contrary to the standard predictions of stellar evolution theory. We show how a simple consistent mechanism, namely…
During the era of primordial nucleosynthesis the light elements 2H, 3He, 4He, and 7Li were produced in significant amounts and these abundances have since been modified primarily by stars. Observations of 3He+ in HII regions located…
The $^3$He isotope is important to many fields of astrophysics, including stellar evolution, chemical evolution, and cosmology. The isotope is produced in low-mass stars which evolve through the planetary nebula (PN) phase. $^3$He…
We follow the evolution of 3He in stars of mass 0.8 -- 10 M (solar units) for Pop. I and II compositions from the main sequence until advanced stages on the AGB. Under standard assumptions we confirm earlier results of more restricted…
Context. The 3He content of Galactic HII regions is very close to that of the Sun and the solar system, and only slightly higher than the primordial 3He abundance as predicted by the standard Big Bang nucleosynthesis. However, the classical…
New stellar models which track the production and destruction of $^3$He (and D) have been evolved for a range of stellar masses $(0.65\leq M/M_{\odot}\leq 100)$, metallicities $(0.01 \leq Z/Z_{\odot} \leq 1)$ and initial (main sequence)…
We use the Green Bank Telescope to search for $^3He^+$ emission from a sample of four Galactic planetary nebulae: NGC 3242, NGC 6543, NGC 6826, and NGC 7009. During the era of primordial nucleosynthesis the light elements $^2H$, $^3He$,…
The uncertainties which still plague our understanding of the evolution of the light nuclides D, 3He and 4He in the Galaxy are described. Measurements of the local abundance of deuterium range over a factor of 3. The observed dispersion can…
We consider the galactic evolutionary history of \he3 in models which deplete deuterium by as much as a factor of 2 to $\sim$ 15 from its primordial value to its present day observed value in the ISM. We show that when \he3 production in…
Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all low mass giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the 3He(3He,2p)4He…
The prediction of standard chemical evolution models of higher abundances of He3 at the solar and present-day epochs than are observed indicates a possible problem with the yield of He3 for stars in the range of 1-3 solar masses. Because…
We examine the stability and observational consequences of mixing induced by 3He burning in the envelopes of first ascent red giants. We demonstrate that there are two unstable modes: a rapid, nearly adiabatic mode that we cannot identify…
Low-mass stars, ~1-2 solar masses, near the Main Sequence are efficient at producing 3He, which they mix into the convective envelope on the giant branch and distribute into the Galaxy by way of envelope loss. This process is so efficient…
Thermohaline mixing has recently been proposed to occur in low-mass red giants, with large consequence for the chemical yields of low-mass stars. We investigate the role of thermohaline mixing during the evolution of stars between 1Msun and…
The cosmic abundance of the 3-He isotope has important implications for many fields of astrophysics. We are using the 8.665 GHz hyperfine transition of 3-He+ to determine the 3-He/H abundance in Milky Way HII regions and planetary nebulae.…
Recent studies of low- and intermediate-mass stars show that the evolution of the chemical elements in these stars is very different from that proposed by standard stellar models. Rotation-induced mixing modifies the internal chemical…
The $^3$He isotope is important to many fields of astrophysics, including stellar evolution, chemical evolution, and cosmology. The isotope is produced in stars which evolve through the planetary nebula phase. Planetary nebulae are the…