Astronomy question from test? answer fast please?

I am studying for my astronomy final and i want to know what are the correct answers to the following questions..I got these wrong. if you know the answers please respond. Thanks in advance. Also feel free to answer any one ..Thanks alot to the yahoo astronomy community!!!!





1)Which of these is the likely progenitor of a type II supernova?


a)an evolved blue supergiant that is about to experience the helium flash


b)two white dwarfs in a contact binary system


c)a mass-transfer binary, with the white dwarf already at 1.3 solar masses


d)a contact binary, with the neutron star at 2.3 solar masses


e)an evolved red giant which is just starting to make silicon in its core





2)Which of the following best describes the evolutionary track followed on the H-R diagram for the most massive stars?


a) horizontally right, then forms a clockwise loop


b)horizontally right, diagonally to lower left, then horizontally right


c)diagonally to lower right, then vertical, then horizontally left


d)horizontally right


e)vertically upward, along the left edge of the diagram











3)Just as a low-mass main sequence star runs out of fuel in its core, it actually becomes brighter. How is this possible?


a)The core contracts, raising the temperature and increasing the size of the region of hydrogen shell-burning.


b)It explodes.


c)Its outer envelope is stripped away and we see the brilliant core.


d)It immediately starts to fuse helium.


e)Helium fusion gives more energy than hydrogen fusion does, based on masses.








4)What can you conclude about a Type I supernova?


a) The star never reached the Chandrasekhar Limit.


b)It was originally a low-mass star.


c)Its core was mostly iron.


d)It was originally a high mass star.


e)Its spectrum will show large amounts of hydrogen.|||1e)an evolved red giant which is just starting to make silicon in its core





This one comes closest. A Type II SN is a massive star, with an iron core collapsing under its own weight. The iron was made by silicon fusion. 1c) is the progenitor of a type I SN





2e first (all stars do that), followed by 2a) Take a look here: http://www.strangehorizons.com/2000/2000鈥?/a>





3a) The core contracts, that increases the central temperature and as a result a larger part of the star is hot enough to sustain fusion.





4 A type 1SN is a dwarf in a binary receiving mass from the other star, pushing it over the Chandrasekhar Limit. So 4b) is correct. 4a) is utterly nonsense and the other 3 are valid for Type II SNs.





Good luck!|||sorry it to borring|||Question 1) "A" ( Type Ib and Ic supernovae are a type of core-collapse supernova for a massive star that has shed its outer envelope of hydrogen and (for Type Ic) "helium".)





Question 2) "E " ( The observed group is then shifted in the "vertical direction", until the two main sequences overlap. )





Question 3) "B " ( Within a few seconds, a substantial fraction of the matter in the white dwarf undergoes nuclear fusion, releasing enough energy (1鈥? 脳 1044 joules) to unbind the star in a supernova explosion. An outwardly expanding shock wave is generated, with matter reaching velocities on the order of 5,000鈥?0,000 km/s, or roughly 3% of the speed of light. There is also a significant increase in "luminosity", reaching an absolute magnitude of -19.3 (or 5 billion times brighter than the Sun), with little variation.





Question 4) "C" ( The core collapses in on itself with velocities reaching 70,000 km/s (0.23c),[59] resulting in a rapid increase in temperature and density. The energy loss processes operating in the core cease to be in equilibrium. Through photodisintegration, gamma rays decompose "iron" into helium nuclei and free neutrons, absorbing energy, whilst electrons and protons merge via electron capture, producing neutrons and electron neutrinos which escape.





There seems to be a couple of words in the selected answers that give credence to the questions that help to give the correct answer. I have selected the ones that seems to fit your criteria and that correspond to those selections. I have put in quotation marks " " the words that fit for your edification. Some of the answers are very close and could be used and be correct depending on the nova or supernova type, (e.g. Type 1, 1a, 1b, 11P and 11L ) there are several that could be used.





I hope this helps you.


Regards,


Warren