Tue, 05/12/2020 - 18:58
In 2015 an observing campaign was launched to observe the T Tauri star RW Mon in support of research being carried out by Dr. Hans Moritz Günther. The campaign was extended to request long term monitoring - that request is still active. Please see AAVSO Alert Notice 514 for details and observing instructions. This forum thread is being created now to allow for discussion, etc. (the campaign predated the existence of our forums).
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
I requested AAVSO help for RW Aur back in 2015. RW Aur continues to be a very interesting target with a lot of changes happening that we don't understand and we don't know when (if ever) it will return to its normal state.
I'm working on a new publication on RW Aur based on new Chandra and AAVSO data from 2018 and 2019 right now. AAVSO data from the campain so far are included in https://ui.adsabs.harvard.edu/abs/2018AJ....156...56G/abstract, a few AAVSO observers are co-authors on that paper.
Since we don't know how RW Aur will change in the future, it's important to continue looking! We believe that an accretion event such as this might also trigger outflows in the jet. The jet has several knots, and one theory is that those knots are formed when more material falls onto the star - and "more material onto the star" is observed as a drop in the lightcurve, because this additional material obscures the star.
So, please keep looking and feel free ot post here with any specific questions. I'll update this thread when I learn more!
X-ray observations are hard to come by because there is only one X-ray observatory in orbit, that can separate RW Aur A and RW Aur B - the Chandra X-ray observatory. Chandra is one of NASA's great observatories, like e.g. the Hubble Space Telescope, and astronomers fomr all over the world ask for observing time on Chandra.
Still, RW Aur has been observed in X-ray several times. The first Chandra ob- servation was taken in 2013 when RW Aur A was in a bright state, the second in 2015 after RW Aur became fainter. We observed it three more times (Jan 2017, Nov 2018, Dec 2019) during the most recent dimming event. RW Aur A’s spectrum looks markedly different at every epoch. No other T Tauri star is known to go through such a wide range of X-ray spectral shapes in just a few years.
In 2013, RW Aur A was in an optically bright state and was undisceranable from other CTTS. It showed signatures of magnetic activity, moderate reddening and an overabundance of neon and underabundance of iron, typical for a classical T Tauri star observed in X-rays. In contrast, the 2015 dim state is characterized by such an increase in reddening that the star is barely detectable. In 2017 the absoorption increased to about 400 times its original 2013 value and we detected a strong emission feature of iron, which means that significantly more iron was in the atmosphere than before. In 2018, we also observed unusual Si and Ca emission.
Two scenarios are consistent with our data. The first scenario is that two large planetesimals collided in 2014 and possibly again at the end of 2016 releasing a cloud of large rich grains that cause reddening, and increase the coronal abundance of grain forming elements when they are accreted.
Images and Chandra press release are here: https://www.chandra.harvard.edu/photo/2018/rwaur/
with a video here: https://youtu.be/MY-y_bhhULM
An alternative scenario is accretion from a so-called "pressure trap". Thick disks can contain deadzones particles > 1 mm will be trapped. If, for some reason, the disk structure changes and that trapped material is released, this might supply enough large grains to explain the extra absorber.
We suspect that RW Aur A is only partially hidden behin all this extra absorber and that ther are occasional "holes" in the screen where some light shines through, maybe only 2-3 %. The shape of the optical lightcuves should show "holes" or "gaps" opening and closing as teh cloud moves around the star if that's true. This is where data from AAVSO observers is really valuable, because in e.g. V or R you can take an image of RW Aur several times per week, while in X-rays, even wit ha telescope as advanced as Chandra, we need to expose for almost a day to collect enough X-rays to say anythign useful and, for an observatory like Chandra, we are lucky if we can convice NASA to put RW Aur on the target list even once per year. Thanks a lot for supporting these observations!
Just some advance notice: We'll perform X-ray observations of Rw Aur again. I just signed off on the parameters and the observations not go into Chandra's queue. Most likely, the obsrvations will be scheduled in December. I'll post here when I knkow more. If would be great to get some optical data in the nights before and after.
I just received notice that our new Chandra observations of RW Aur have been scheduled for the following dates (list gives start time in UT, each observation is a few hours long):
Optical data close to these times would be very helpful!
What filters and cadence of observations would be most helpful to you to correlate with the Chandra observations of RW Aur?
AAVSO Alert Notice 727 requests coverage of the T Tau star RW Aur in support of Chandra observations taking place December 7, 13, 1nd 15 UT. Please see the notice for details and observing instructions. This request is part of the campaign on RW Aur that began in 2015 (AAVSO Alert Notice 514).
Please subscribe to this thread if you are participating in the campaign so you can be updated by the astronomer and by HQ. Join in the discussion or ask questions there!
Many thanks, and Good observing,
Elizabeth O. Waagen, AAVSO HQ
For operational reasons, Chandra needs to split the observations into more pieces. I don't yet have final dates for the last set of observations, but I know that it will continue after 2020-12-15, likely into the next two-week block, which would last till about 2020-12-27.
Thus, if would be great if you can continue to monitor RW Aur until the end of December. I'll post updated Chandra observing dates here when I get them.
RW Aur looks like it brightened by .25 mags last night in all 4 colors BVRI. Submitted to the AID. I will stay on it until the end of Dec. I have it every clear night right now.
Cool! I've seen the Chandra preview images and it looks like it's brigther than in previous years there, too. Details have ot wait until I get the full data.
It's getting even brighter in all bands. At the moment I have found it at ~10.7V.
2020-12-28 00:00:00 (nominal, might be rescheduled)
(All times in UTC)