This is a test case for how open science could work.
During the 18th European White Dwarf Workshop I started
thinking what happens to a 0.5 solar mass helium core white dwarf when
it accretes matter from a companion and goes over the mass limit where
it should turn into a C/O core white dwarf? Does it start to fure helium
into carbon and oxygen at the core? How does this affect the star? Does
it expand and become a giant star for awhile? Does it explode? And on
the population side, are these kinds of stars common enough that we
should see them?
Does anyone have a model that could be used to test this? Would it be very difficult to modify a model designed for studying the collapse of a C/O core WD to work with a He core WD?
ReplyDeleteHi Tommy
ReplyDeleteFirst of all thanks for starting this web site and the WD open science project. I will try to help answering this question.
I guess the first thing we should take into account is what kind of accreting WD binaries exist. I can think of four types: cataclysmic variables, AM CVn stars, symbiotic binaries and super-soft X-ray sources (SSS).
The WD masses in CVs are generally quite high (~0.8Msun) so can be excluded here.
In AM CVs stars the donor is generally the lower mass WD because its bigger and fills its Roche-lobe. Maybe the question here would be the other way around, what happens if a CO core WD losses so much mass that it becomes a He core WD?
In SSS the mass ratio is q ~ 1 and since the donor is a G or K star, then the WD should be also massive.
Symbiotic stars however apparently can have He core WD accretors. I dont know much about these binaries but the question here would be whether or not the mass transfer rate is high enough to build up material on the WD and whether or not nova outbursts are regular.
I hope it helps!
Alberto
Ok,
ReplyDeleteSo, it is not sure if we can even have a He-core WD accreting mass in a way that could produce CO core. What would it take to have such a system? Is it even possible? Since I'm not an expert on binary evolution, I can't really say anything definite about it.
And we could also think about the original question just *assuming* that such a thing could happen.
I would also like to ask, if there is a low mass tail in the mass distribution of CVs?
Hi,
ReplyDeleteI'm not a white dwarf researcher but I came across your conference proceedings on arXiv and I'm curious to see how this project pans out.
To contribute, your question of "what happens when a 0.5 solar mass He WD accretes enough to start fusing helium?" can probably be answered by a new stellar evolution code, MESA [1,2]. It was recently used to model classical novae [3] and the test cases [4] include the creation of He WDs.
The code is completely free and open source so you can download it and start experimenting straight away. There's also a fairly lively code community developing. I currently use a different stellar evolution code but you should try MESA because it can clearly handle some WD modelling.
[1] http://mesa.sourceforge.net
[2] http://mesastar.org/
[3] http://arxiv.org/abs/1210.5209
[4] http://mesastar.org/documentation/tutorials/white-dwarf-test-cases
Oh yes,
ReplyDeleteI think someone mentioned MESA during the conference in Krakow. I hope I will have a chance to try it soon. Or maybe someone else has time to do it right now...
In the mean time, there was a paper on arXiv today reporting on a post-common envelope binary (http://arxiv.org/abs/1210.6532). Going through it I checked a reference that has modelling on accreting binaries with a He-core. Here is the ADS link for the paper: http://adsabs.harvard.edu/abs/2009ApJ...705..693S
Interestingly, at the end of section 5.1 the authors mention that the code they were using did not take into account the possibility of the core temperature rising enough to ignite the core. However, they think that it would be interesting to study that possibility too.
Hi Tommi
ReplyDeleteSorry for my ate reply. You can have a look at the following paper to see the mass distribution of CVs
2011A&A...536A..42Z by Zorotovic et al.
Cheers,
Alberto
Hi
ReplyDeleteThe future of the WD depends ond many things like the WD mass, accretion rate, and also the composition of the accreted material.
Even if a He WD accretes enough material to exceed 0.5 Msun, I don't think that the rise in the temperature is enough to convert all the He in C/O (maybe only in an outer shell), so my guess is that it will be still a He WD but more massive.
Some authors claim that He WDs can accrete material only until they reach a certain mass (~0.7 Msun) when the WD explotes as a SNe. You can check these two papers:
http://adsabs.harvard.edu/abs/1977PASJ...29..765N
http://adsabs.harvard.edu/abs/1986ApJ...301..601W
I hope it helps (I haven't found any recent simulations, so if you do please let us know).
Regarding the WD masses in CVs, there are a few with Mwd < 0.5 but the mass estimation is not accurate at all. There is not a singLe system with a confirmed He WD, while the simulations predict a lot of them, which may imply that WDs in CVs really accrete mass.
Cheers,
Monica