B[e] star IRAS 17449+2320: call for observations

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Re: B[e] star IRAS 17449+2320: call for observations

Postby Francisco Campos » Sat Jun 17, 2017 10:09 am

Hi, James,

unfortunately the AAVSO has not a good sequence for this star, unless you use a wide-field scope or a big sensor CCD. I have only a night of V-photometry taken with a 8" RC scope, working a f/5.3 and a ST-8XME CCD (KAF 1603-ME). This set-up covers 40'x26', more or less. I hesitated between this set-up or a ED 66/400, but the ED I think it's too small to get a good S/N. A good alternative should be a 100 or 120mm f/5 achromatic refractor or a 150-200 mm reflector.

Without a good sequence. i choosed UCAC4 568-061583 (mag. 9.51, B-V=0.66, according to APASS catalogue) as comparison star and UCAC4 568-061635 (mag. 10.49, B-V=0.46) as check. Exposures of 120" gave me about 25000 ADU's with the ST-8 slightly defocused and an acceptable dispersion.

Hope this one will help you.

Greetings
Fran
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Re: B[e] star IRAS 17449+2320: call for observations

Postby Olivier GARDE » Sun Jun 18, 2017 10:07 am

Evolution of this star since 7 days

H Alpha
Image

H Beta
Image

H Gamma
Image
LHIRES III #5, LISA, e-Shel, C14, RC400 Astrosib, AP1600
http://o.garde.free.fr/astro/Spectro1/Bienvenue.html
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Re: B[e] star IRAS 17449+2320: call for observations

Postby Francois Teyssier » Mon Jun 19, 2017 4:45 pm

Congratulations to all!

Steve answers: "Not clear"
(to be published in the next issue of the letter - But I'm late: two much spectra of AG Dra !!!)

IRAS 17449+2320 and other misdemeanors
The sequences in this issue for this B[e] star shows a progressive line pro le change that's been
seen in other members of this group of stars whose origin, quite simply put, is not clear. As the
phrase goes, \that's why it's called `research"'. The red wing, and the shift in the absorption feature
on the blue and red sides of the Balmer lines, is not seen on all transitions. For example, in this
star the O I 7772 and 8446| multiplets show emission that seems stationary about the system
radial velocity and a core than also remains stationary but sometimes show a displaced absorption
feature at almost 150 km/s on the redward side. Or sometimes on the blueward side but usually
not. The core depression is really an absorption line, not merely a lack of emission (this has been
often interpreted in these stars as a simple disk-like emission pro le with two peaks from the orbital
motion). That isn't the case here, emission is detected at the same radial velocity for the Paschen
lines as the absorption in the Balmer lines. So the absorption in one is pumping emission from the
other. This relates directly to the Balmer decrement I've discussed here. The absorption of the
higher lines is weak so the photons escape but it isn't zero. Some self-absorption leads to escape of
photons from the de-excitation of the upper levels. This is a process very much like what you see in
the Fe curtain stage of novae and will require a bit more time to explain (hence stay tuned). But why
the red wing should be the only part that varies, or varies more dramatically, is not obvious. If it's
dust, as for novae, it's even harder to explain because in a disk no structure can remain stationary
in angle. It may be that the disk is warped, and precessing. Or there may be structures provoked
by he presence of a binary star companion. None of these explanations is yet excluded and because
this is a stochastic (not always seen) phenomenon, it's very important to follow it. I'll make the
same comment for these stars as for novae. One of the most serious lacunae in our understanding of
time variable cosmic phenomena is long term time series. Most observatories (and time allocation
committees) lose patience with things that take years. Weather is one thing, access another. Your
continued interest in, and monitoring of these stars (and all of the hard work you've been ding) ll
gaps, producing a permanent record of long term behavor for which the future will be grateful!
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Re: B[e] star IRAS 17449+2320: call for observations

Postby Francisco Campos » Mon Jun 19, 2017 6:17 pm

Good explanations, François, a bit hard to understand but always interesting.

Here is a comparison between two nights. Even at low resolution it is clearly noticeable the changing profile of the H-beta band. But I'm worried about the striking difference between both profiles in the blue wavelengts, while in red wavelengs the match is almost perfect. The comparison star (HD 157728, A7 V) is the same, also the spectrograph and CCD. Te telescopes used are different: newton with Barlow lens the first one, and a RC the second.

Any idea? Are these differences real? Maybe a bit of B-band photometry could give a clue...

iras17449+2320_ 20170618_890_FPC.png

Greetings
Fran
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Re: B[e] star IRAS 17449+2320: call for observations

Postby Francois Teyssier » Tue Jun 20, 2017 5:06 pm

From Steve, about Photometry:

The problem is that except for Tycho there's almost nothing on this star, Francois. Korcakova has an amateur who's been getting occasional photometry but I have no idea how that's being reduced, what filters
(manufacture) are being used (other than being generically called V and R), or what the standards are. I'll check. In SIMBAD there are a stars that might serve, likely not variables (but internal checks take care of that), most are from Tycho and are on the faint side (most are fainter than V ~ 11) but a few are comparable brightness and would likely be in the same CCD field (at 10 min there aren't many and they're faint, at 20 arcmin the list expands considerably). From what we can see, the amplitude is quite small, no more than a few tens of millimags, but we don't really know what to expect. Having BVR would be much more useful since the R filter contains Halpha and that's very strong relative to the continuum (variability could be accounted for by that line alone, for instance, if you push the interpretation).


Fran: looks to be a severe issue with instrumental/atmospheric correction

François
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Re: B[e] star IRAS 17449+2320: call for observations

Postby Francisco Campos » Sun Jun 25, 2017 5:49 pm

Francois Teyssier wrote:From Steve, about Photometry:
Fran: looks to be a severe issue with instrumental/atmospheric correction
François


Hi, François

I'm quite worried about this issue. The last night, by a suggest of Joan Guarro, I took another spectrum but with two comparison stars: HD 157728 (A7 V, the star I use regularly, green spectrum) and pi Ser (HD 143894, A3 V, dark spectrum). The spectra obtained are a bit different, as yo can see here.

All spectra are, of couse, flat-field corrected, average of 20 flats exposed at 2/3 of the full histogram. But of course, at short wavelengths the response is lower.

iras17449+2320_ 20170623_996_FPC.png


I have been comparing spectra of T CrB processed with Pi Ser and they match almost perfectly in all wavelengths, so I don't really understant what's happening.

By the way, interesting the behavior of the H-beta band, changing every few nights.

iras17449+2320_ 20170623_996_FPC Hbeta.png
iras17449+2320_ 20170623_996_FPC Hbeta.png (25.41 KiB) Viewed 296 times


Greetings
Fran
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Re: B[e] star IRAS 17449+2320: call for observations

Postby Francois Teyssier » Mon Jun 26, 2017 5:30 am

Hello Fran,

This is atmopheric correction
Such variations of the continuum are not expected for that star
More, important variations would produce large variation of the luminosity; this not the case.

Nice variations of the lines!

All the best,

François
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