Disks and things

Paddling has been wearing me out. We have practice every day for about an hour and half. On Thursday and Friday last week we paddled 4.5 and 3.5 miles respectively and now we’ve gotten into to doing half mile sprints. I have gotten to the point where whileI’m not horribly sore the next day which is really satisfying it still takes a lot out of me. Our regatta is this Sunday and then that’s the end of it. It’s been a ton of fun be out on the bay every day but I’m looking forward to be back to normal energy levels.

I spoke with Bernadette again on Monday. I updated her on the papers I have been reading and the conversation I had with Vladimir. She was particularly interested in the Grinin paper that proposed the binarity of RR Tau. I need to email her the reference so she can take a look at it. I have a few questions on that paper and it would be good if she can answer them.

For most of our conversation we talked about what kind of data I want to get focusing on what wavelength region I should be interested in. In her 2002 paper Bernadette detected about 15 features over a large wavelength range. We decided we wanted to focus on a smaller wavelength range, and thus less features, so we can get higher resolution data. My job is to play with the Integration Time Calculator and decide the observing parameters: the best grating, wavelength range, etc…Then I’m going to write the proposal for time despite the fact that it doesn’t need to be submitted until August when RR Tau finally comes back up. I’ve never written a proposal before so it seems best to start as soon as possible so I can get feedback and make sure everything is correct so when it’s time of submission I can do it immediately.

Bernadette sent me a research statement she wrote a few years back about some high resolution spectra of RR Tau she obtained but never published.

Two Fe II lines overlaid in velocity space.

In the statement Bernadette reiterates the key point made in her 2002 paper, that the spectral signature of RR Tau changes with continuum variations. When the star is at its brightest there are strong metallic absorption lines and at its dimmest there are faint metal emission lines that are associated with the stellar photosphere and an optically-thin disk atmosphere respectively. Understanding this is completely tied to understanding the nature of the obscuring material. What is it made of? How does it move? Evolve? What is it’s structure?

The general outline of discerning the fundamentals of the obscuring material is to use the characteristics of the light curve with spectral information to constrain models which has been fairly rudimentary. I think it will be a real step up to use narrow band filters along with spectroscopy. Also, depending on the resolution we’re able to obtain we might be able to resolve the disk in greater detail than what has been previously managed.

Literature Review #2: Is RR Tau a binary?

On the Nature of Cyclic Light Variations in UX Ori Stars
Grinin et al., Astronomy Letters

Vladimir Grinin is a name that often pops up when looking into UXors. He has been studying them for decades which is quite an advantage in variable star research. He had his his co-authors conducted decades long photometric monitoring on many UXor type stars that produced a series of papers. This paper is the first in the series and includes the results for RR Tau.

They observed RR Tau for 673 nights spanning 30 years. They found evidence of possible periodicity on timescales of ~8.6 and ~3.4 years. As far as I know this is the first discussion of long photometric variability in UXors and something I haven’t really seen discussed until the Maria Mitchell paper. It is interesting to me that our timescales are so different. The long term variability that we discussed in our paper was on the order of 100 days but Grinin et al. are talking about many years. I doubt that this has anything to do with the mechanism of variability that I want to look into for my thesis but it is fascinating to add another layer of complexity to this stellar system.

The change in continuum light over time.

The above figure is from a small review paper they wrote summarizing all their results.

The authors attribute the variation to binarity mostly because it is periodic and because the percentage of binary stars among Herbig Ae/Be is high. From what I can tell from their paper that they don’t directly attribute the periodicity to the companion star passing infront but rather the companion star is disrupting the the column density of the circumstellar disk. They go onto assert that the a binary system accounts for the short term activity that characterizes UXors also because of disruptions. This possibility could be relevant to my investigation on the medium term timescale.

I don’t understand the differing timescales they report, I don’t see that in the light curve. I’m going to read the other papers in the sereis and see if they shed so light on it.