Is this how a Super Nova works?

[Pluto]

G'day from the land of ozzzzzzzzzz

 

I just cannot stop reading papers on cosmology. It must be a sickness of some sort.

 

It does not matter how many papers I read. I find myself knowing less. Now try to work that out.

 

I could comment on the paper, but the abstract explains.

 

[0711.2417] Diffuse interstellar medium and the formation of molecular clouds

Diffuse interstellar medium and the formation of molecular clouds

 

Authors: P. Hennebelle, M.-M. Mac Low, E. Vazquez-Semadeni

(Submitted on 15 Nov 2007 (v1), last revised 26 Nov 2007 (this version, v2))

 

Abstract: (Abridged) The formation of molecular clouds (MCs) from the diffuse interstellar gas appears to be a necessary step for star formation, as young stars invariably occur within them. However, the mechanisms controlling the formation of MCs remain controversial. In this contribution, we focus on their formation in compressive flows driven by interstellar turbulence and large-scale gravitational instability. Turbulent compression driven by supernovae appears insufficient to explain the bulk of cloud and star formation. Rather, gravity must be important at all scales, driving the compressive flows that form both clouds and cores. Cooling and thermal instability allow the formation of dense gas out of moderate, transonic compressions in the warm diffuse gas, and drive turbulence into the dense clouds. MCs may be produced by an overshoot beyond the thermal-pressure equilibrium between the cold and warm phases of atomic gas, caused by some combination of the ram pressure of compression and the self-gravity of the compressed gas. In this case, properties of the clouds such as their mass, mass-to-magnetic flux ratio, and total kinetic and gravitational energies are in general time-variable quantities. MCs may never enter a quasi-equilibrium or virial equilibrium state but rather continuously collapse to stars.

[maddog]

It's a common misconception that Pop I stars were first and Pop II stars were last but the Pop II stars were first and Pop I stars were last.

It is not likely this had changed in the last thirty years or so. I might have

my wires crossed (Pop I / Pop II).

New thought seems to point out there needed to be Pop III stars (figuring from the same premise) Pop III stars would have been the very first Stars, Pop II would have been what we see as the oldest stars now and Pop I stars are the youngest with the highest concentration of metals.

I would like to find the latest data on Pop III stars (not just wiki references).

Could you suggest any.

 

maddog

[Moontanman]

It is not likely this had changed in the last thirty years or so. I might have

my wires crossed (Pop I / Pop II).

 

I would like to find the latest data on Pop III stars (not just wiki references).

Could you suggest any.

 

maddog

 

The Pop III thing kind of took me by surprise too. I have read about the supposed first stars with nothing but hydrogen and helium but this is the first I've heard them called Pop III. Pop II stars have very very low but still detectable amounts of metals. Pop I stars like our sun have significant metals and it affects their entire evolution from start to finish. Pop III star could have been much bigger than any possible Pop I or even Pop II stars due to the lack of metals.

 

PS In this context metals are any element heavier than helium.

[Pluto]

G'day from the land of ozzzzzzzzz

 

I'm reading through some Supernova papers.

 

This is quite interesting

 

[0709.2519] A photometric search for transients in galaxy clusters

A photometric search for transients in galaxy clusters

 

Authors: D.J. Sand, D. Zaritsky, S. Herbert-Fort, S. Sivanandam, D. Clowe

(Submitted on 17 Sep 2007 (v1), last revised 21 Feb 2008 (this version, v2))

 

Abstract: We have begun a program to search for supernovae and other transients in the fields of galaxy clusters with the 2.3m Bok Telescope on Kitt Peak. We present our automated photometric methods for data reduction, efficiency characterization, and initial spectroscopy. With this program, we aim to ultimately identify $sim$25-35 cluster SN Ia ($sim$10 of which will be intracluster, hostless events) and constrain the SN Ia rate associated with old, passive stellar populations. With these measurements we will constrain the relative contribution of hostless and hosted SN Ia to the metal enrichment of the intracluster medium. In the current work, we have identified a central excess of transient events within $1.25 r_{200}$ in our cluster fields after statistically subtracting out the 'background' transient rate taken from an off-cluster CCD chip. Based on the published rate of SN Ia for cluster populations we estimate that $sim$20 percent of the excess cluster transients are due to cluster SN Ia, a comparable fraction to core collapse (CC) supernovae and the remaining are likely to be active galactic nuclei. Interestingly, we have identified three intracluster SN candidates, all of which lay beyond $R>r_{200}$. These events, if truly associated with the cluster, indicate a large deficit of intracluster (IC) SN at smaller radii, and may be associated with the IC stars of infalling groups or indicate that the intracluster light (ICL) in the cluster outskirts is actively forming stars which contribute CC SN or prompt SN Ia.

 

 

and

 

[0709.4025] Uncovering the Chemical Signature of the First Stars in the Universe

Uncovering the Chemical Signature of the First Stars in the Universe

 

Authors: Torgny Karlsson, Jarrett L. Johnson, Volker Bromm

(Submitted on 25 Sep 2007 (v1), last revised 17 Jan 2008 (this version, v2))

 

Abstract: The chemical abundance patterns observed in metal-poor Galactic halo stars contain the signature of the first supernovae, and thus allows us to probe the first stars that formed in the universe. We construct a theoretical model for the early chemical enrichment history of the Milky Way, aiming in particular at the contribution from pair-instability supernovae (PISNe). These are a natural consequence of current theoretical models for primordial star formation at the highest masses. However, no metal-poor star displaying the distinct PISN signature has yet been observed. We here argue that this apparent absence of any PISN signature is due to an observational selection effect. Whereas most surveys traditionally focus on the most metal-poor stars, we predict that early PISN enrichment tends to `overshoot', reaching enrichment levels of [Ca/H] ~= -2.5 that would be missed by current searches. We utilize existing observational data to place constraints on the primordial initial mass function (IMF). The number fraction of PISNe in the primordial stellar population is estimated to be <0.07, or ~< 40% by mass, assuming that metal-free stars have masses in excess of 10 M_sun. We further predict, based on theoretical estimates for the relative number of PISNe, that the expected fraction of second generation stars below [Ca/H]=-2 with a dominant (i.e., >90%) contribution from PISNe is merely ~1e-4 - 5e-4. The corresponding fraction of stars formed from gas exclusively enriched by PISNe is a factor of ~4 smaller. With the advent of next generation telescopes and new, deeper surveys, we should be able to test these predictions.

[CraigD]

Pop I stars are initial life stars (only original elements from the birth of the big bang).

 

Pop II stars were created from the medium of previous Supernovae.

As everyone has already noted, Maddog has the idea right, but the numbering scheme backwards.

 

Population I stars are the most recently formed, and thus have a higher concentration of metallic elements than other, older stars. Our Sun in population I.

 

Population II stars are older, and thus have lower metallicities. There aren’t as many of these stars in our vicinity (the Milky Way galaxy and its halo), because they tended to be large, powerful, and short-lived. Those that still exists are small (around 1 solar mass or less) and not very powerful. Many are found in globular clusters, which appear to consist almost entirely of Population II stars.

 

Population III stars are hypothetical, as none have been unambiguously observed, and are expected to be very distant. By definition, Population III stars have not metallic elements in them, except at the very ends of their lives, which are expected to have been very short. By definition, according to conventional theory, Population III stars were the first to have formed.

 

When last I kept up with observational astronomy enough to have much of a feel for it (in my late teens and early 20s, when I was lucky enough to intern at an observatory, and was considering becoming an astronomer), three was a good bit of surprise that successive generation of deep-field spectroscopy hadn’t found, at the edge of visible space, Pop III stars (recall that, per mainstream theory, the edge of visible space equates to the earliest years of the universe). The general sentiment is that probably, they had been, but were showing false absorption lines because there was so much interstellar medium between them and us. Since then (ca 1980), there’s been a lot of work attempting to use effects like gravitational lensing to compensate for such effects, but, as best I can tell, no great success.

 

A star of any population can end in a supernova, as long as it’s massive enough. Nearly all of the metal in population II and I stars, as well as the metal found on Earth and other planetary bodies is thought to have been created by supernovae.

[Pluto]

G'day from the land of ozzzzzzzzzz

 

Sorry for posting links. For the next two years I will be in this frame of mind. Until I can understand.

 

[astro-ph/0511628] Do recent supernovae Ia observations tend to rule out all the cosmologies?

Do recent supernovae Ia observations tend to rule out all the cosmologies?

 

Authors: Ram Gopal Vishwakarma (Zacatecas University)

(Submitted on 21 Nov 2005 (v1), last revised 18 Jan 2008 (this version, v4))

 

Abstract: Dark energy and the accelerated expansion of the universe have been the direct predictions of the distant supernovae Ia observations which are also supported, indirectly, by the observations of the CMB anisotropies, gravitational lensing and the studies of galaxy clusters. Today these results are accommodated in what has become the `concordance cosmology': a universe with flat spatial sections t=constant with about 70% of its energy in the form of Einstein's cosmological constant Lambda.

However, we find that as more and more supernovae Ia are observed, more accurately and towards higher redshift, the probability that the data are well explained by the cosmological models decreases alarmingly, finally ruling out the concordance model at more than 95% confidence level. This raises doubts against the `standard candle'-hypothesis of the supernovae Ia and their use to constrain the cosmological models. We need a better understanding of the entire SN Ia phenomenon in order to have cosmological consequences from them.[/QUOTE]

 

How can this be so?

 

If the Condordance model is ruled out, what does it mean?

[Pluto]

G'day from the land of ozzzzz

 

Somtimes I see comments on topics and relate the paper to it.

 

I tripped over this paper by accident, I hope this maybe of interest.

 

[0806.3697] The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars

The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars

 

Authors: Takuma Suda (1), Yutaka Katsuta (1), Shimako Yamada (1), Tamon Suwa (2), Chikako Ishizuka (1), Yutaka Komiya (3), Kazuo Sorai (1), Masayuki Aikawa (1), Masayuki Y. Fujimoto (1) ((1) Hokkaido Univ., (2) Tsukuba Univ., (3) Tohoku Univ.)

(Submitted on 23 Jun 2008 (v1), last revised 28 Jun 2008 (this version, v2))

 

Abstract: We describe the construction of a database of extremely metal-poor (EMP) stars in the Galactic halo whose elemental abundances have been determined. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the recent literature that report studies of EMP halo stars with [Fe/H] < -2.5. The compilation procedures for this database have been designed to assemble the data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria, and permits the user to explore relationships between the stored variables graphically. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering all of the relevant papers published by December 2007. We discuss the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe/H] < -2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amount to ~30 % for [Fe/H] < -2.5. We find that known binaries exhibit different distributions of orbital period, according to whether they are giants or dwarfs, and also as a function of metallicity, although the total sample of such stars is still quite small.