T CrB increase in the UV

[Peter Somogyi]

Hello,

I've observed in the past 2 days that T CrB become prominent in the UV down to 3620A (unsure exactly when) during the past year, and it seems to be unusual when browsing back in the ARAS DB (or maybe just this region is missing):

UV-end now vs year ago

tcrb_alpy_UV_3620A.png (49 KiB) Viewed 6572 times

In order to doublecheck calibrations before reporting this UV event (IR, wavelength of the Alpy), I've made an experiment repeating the range 3620A - 4200A by using LHires 600/mm 35u slit (3 x 20 minute of LHires vs 3 x 5 minute of the Alpy):

LHires 600/mm R~1000 average resolution (should be much more in the middle)

tcrb_alpy_vs_LHires600.png (43.58 KiB) Viewed 6572 times

I did take care of enlarging width for gathering up defocused photons at the edges, resolution is best in the middle.
Also made several checks with the LHires (taken also Vega for IR calibration) about wavelengths.
It works also as a proof now that my Alpy still properly calibrated for wavelength in the UV.

In case this UV increase would turn to be important, please let me know.

- Peter

[James Foster]

To: Peter,

Based on your results and the relative clear skies last night I took a 90min (6x900sec) shot of this object around CaK:

Here is another (not re-sampled) plotted in PlotSpectra that has some more interesting lines not shown above:

The H-eps & H-zeta lines are very prominent and some He lines apparent as well.
I will try to do this again with longer exposure and maybe in the H10 region, but its hard since dawn comes up when this object is only
70 min west of meridian.

James

[Peter Somogyi]

Thank you James, however my "alert" here is rather unofficial, and might be coming from a processing artifact at the UV edge (the continuum tail below 3720A I'm referring to).
Indeed, I did find some of earlier spectra similar to this (e.g. asdb_tcrb_20180323_032.fits - also mine, nicely reproducing) so it's definitely not new, and currently investigating whether the changes are real at all, or a known behavior of T CrB.

Typically Alpy/Dados that seem to have usable UV end in the database to confirm this tail-move-up, and I plan further observational effort (long exposures burning in H-alpha) when having the Alpy mounted again. This time it was very short (3 x 5 min) till clouds suddenly arrived.
Hope I can gather and prepare some presentation later, to compare the data more comprehensively.

As for your result, it's the 1st high resolution CaII region I can see - just the CaII feature is missing or weak in general here. There's an extra line at 3870A that I'm curious about.

Cheers,
Peter

[Francois Teyssier]

Hi Peter,

Great results
Munari & al. (2015) describe the current state of T CrB as "superactive". Among the characteristics : strong He II > H gamma and strong Bowen blend (4640 A)
The comparison of the spectra between low and active states show a strong Blue/Near UV continuum.

TCrB_.JPG (39.75 KiB) Viewed 6427 times

The spectrum you obtained in march 2018 matches well with the continuum obtained by Munari.
Considering the evolution of B-V index, I think that there's no significative change since 2017

TCrb_BV.JPG (30.84 KiB) Viewed 6427 times

A significant change of the continuum (as seen in your comparison) should provoque a significant change of B-V Index

The current improvments in near UV (your work on VV Cep, UVEX by Christian ...) are of great importance for many spectroscopic studies, notably Symbiotics.
This a a key point. Low res observers, especially with Alpy, should focus on this part of the spectrum, with an improved instrumental response (hard task regarding the low sensitivity of our CCD)

3869 is [Ne III], a very important diagnostic line. The other part of the doublet, 3968 is blended with H epsilon and Ca II



All the best,

François

[Peter Somogyi]

Hello Francois,

Thank you for the spectrum graph, now I can see how it should look.
Your B-V index graph what I've been searching for some time, curious how you generate it.
However, I am more curious at the Balmer end changes - how real they are -, where interestinig changes occur, breaking the continuum trend that used to be quite stable over a long period in the visual range.
Reusing your B-V index graph, I've generated now colored serie (all rectified to 4149 - 4254 A), each color assigned to an observer:

asdb_tcrb_20180323_032 2458200 3626 PSO purple
asdb_tcrb_20171007_789 2458034 3723 FPC blue
asdb_tcrb_20170629_860 2457934 3545 PSO purple
asdb_tcrb_20170615_134 2457919 3681 GKA red
asdb_tcrb_20170525_968 2457899 3740 MVE brown
asdb_tcrb_20170519_854 2457893 3746 FPC blue
asdb_tcrb_20170506_968 2457880 3722 FPC blue
asdb_tcrb_20170422_906 2457866 3728 FPC blue
asdb_tcrb_20170413_157 2457856 2137 JPG orange
asdb_tcrb_20170409_966 2457853 3733 FPC blue
asdb_tcrb_20170401_018 2457844 3524 PSO purple
<following spectra shown only on the serie graph, out of B-V graph time:>
asdb_tcrb_20160822_925 2457623 3700 CBO brown
asdb_tcrb_20160702_891 2457572 3744 JGF cyan
asdb_tcrb_20160617_137 2457556 3699 GKA red
asdb_tcrb_20160605_165 2457544 3602 GKA red
I've generated the stack plot via PlotSpectra, that uses the leftmost (noisiest) UV pixel data for positioning the label - hence labels not shown in the right order on the graph itself. Same colors per observers should help out here.
I did exclude a few spectra from 2015 because continuum is very much different in general, won't fit in the spectrum serie.

What I finally wanted to show:
1) UV end have had a flatter continuum slope in 2017 (all except 2017.05.19_854 and 2017.10.07 by FPC)
2) get confirms by others, at a wider time coverage
My little practice in the near-UV so far tells, it may behave radically different than the visual continuum, or the B-V index would suggest.

A trick for enhancing this region, you can set the scope focus better for UV (there's a little fishtail after Balmer end - just magnify on live view, logarithmic scaling) whilst the near-IR part getting defocused (it's a fair sacrifice I think, near-IR is useless anyway without order filter).
Those who have bigger CCDs, may need to sacrifice the whole IR above 7600A, in the case you really want to optimize for UV (same I do, with a 2/3" ccd size). I also plan to cut out the H-alpha in future (zeroing out manually on the spectrum - not to get it used by mistake) and take longer exposures.
I don't think it's a matter of ccd sensitivity down to 3500A, rather than focusing tricks and removing disturbing optical elements from the light path (certain reducers).
Once after got usable SNR, yet the calibrations are tricky (I have not settled here yet).

Cheers,
Peter

[Christian Buil]

eShel spectra of T CrB (a faint object for a fiber spectrograph and R=10 000 !) :



A detail of the deep-blue (note the use of a CMOS ASI183MM camera) :



A full range spectrum taken the April 21.8 with the large format ASI1600MM CMOS camera and a modified eShel:



Christian B

[James Foster]

Here's my T CrB spectrum taken on 04Apr18:

Of course, all non-balmer lines are tentative. Looks like T CrB is becoming more acting across the visible and near UV spectrum.

James