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Re: Chromospheric active stars: a key program for amateurs

PostPosted: Mon Apr 22, 2019 1:28 pm
by Benjamin Mauclaire
Hi Peter, Andrew,

Indeed EW depends on line's shape and components.
However most of scientific works need hight resolution spectra to get the most accurate line shape and then measurements over it.
Using to low resolution spectra for research looks to me rather hazardous.

About EW uncertainty computation, T. Eversberg had published a work in 2006 based on Chalabaev paper.
Moreover, EW is, as you said, very dependend on continuum estimation. About 8 years ago I wrote a study about that:
http://spcaudace.free.fr/docs/ew/

Benji

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Mon Apr 22, 2019 6:00 pm
by Christian Buil
Peter, your H&K spectra are excellent !

An important info. Alexandre Santerne, Laboratoire d’Astrophysique de Marseille (Aix - Marseille University, France), involved in the observation of chromospherically active stars for it’s works around exoplanets, suggests a first list of stars to observe. All these targets are known to be bright, member of the main sequence and very active :

HD 166
HD 20630
HD 22468
HD 37394
HD 41593
HD 114519
HD 115404
HD 131156
HD 146361
HD 200391
HD 210334
HD 220140
HD 224085

Once you get your hands on these targets, Alexandre suggest an equivalent list, but rather inactive. If possible, targets should be observed with a resolution of the order of or greater than 10,000 by covering the spectral range between (at least) 3880A and 4020A. It is useful to make time series over several nights to see the variability associated with stellar rotation.

I do not recommend innovating for these measures. Measuring the equivalent width (EW) is not a very good idea at this stage. S-index is important to link your results to past and future measures.

In a personal correspondance, Alexandre Santerne well specifies the protocol, which must be followed: For the exploitation of the spectra, it is advisable (once corrected in radial velocity) to integrate them in a K-domain centered on 3933.664A and of total width 1.09A, and a K-domain centered on 3968.470A and 1.09A total width. It is also necessary to integrate the spectrum into a B and V domain centered on 3901.070A and 4001.070A (respectively) and with a total width of 20A. Then, it is advisable to calculate the value S = (H + K) / (B + V) which will make it possible to follow the variations. Once the S value has been measured, the operation still requires a few small adaptations but we will see these calibration stories later.

Christian

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Thu May 09, 2019 12:55 pm
by Jean-Pierre Masviel
Ksi Boo (HD 131156):

_hd131156_20190501_902_JP MASVIEL.png


Other results and setup informations:
http://astrosurf.com/jpmasviel/201905OHP/201905OHP.html

Jean-Pierre

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Fri May 10, 2019 1:31 pm
by Christian Buil
Jean-Pierre, excellent and exiting !!!

Your H & K spectra are of hight quality (very well resolved... a 19-microns slit !).

I also observed some stars in the Alexandre Santerne list during the same period as you. The comparison is very instructive (I put your data in the same format as mine for easy comparison).

I have a much lower resolution because I took the option to use a wide slit (35 microns), so my resolution is only about R = 6000.

HD1311519 :

Image

HD146361 (double lined H & K emission, and perhaps a spectroscopic double star) :

Image

HD210334 (possible evolution during the 2 days covered period) :

Image

and more at medium resolution:

Image

Image

Image


Jean-Pierre, je me suis permis d'utiliser certains de tes spectres pour illustrer page de présentation du projet H & K :
http://www.astrosurf.com/buil/chromospheric_activity/


The opening of a specific ARAS database will quickly become a necessity to gather all these spectra... !

Christian

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Fri May 10, 2019 2:08 pm
by Robin Leadbeater
Christian Buil wrote:
The opening of a specific ARAS database will quickly become a necessity to gather all these spectra... !



Perhaps the existing BAA database could be used? It is secure long term, has full search functions and a special "chromospherically active" category could probably be set up to keep the observations together.

Cheers
Robin

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Mon May 13, 2019 7:46 am
by Dubreuil Pierre
Bonjour à tous

Hier soir premier essai UVEX3 avec fente claire dans la partie UV.

hd131156 12-05-2019.png
HD 131156 slit 35m
hd131156 12-05-2019.png (110.8 KiB) Viewed 3798 times


Un zoom sur H et K

hd131156 12-05-2019_crop.png
HD 131156 slit 35m crop
hd131156 12-05-2019_crop.png (61.93 KiB) Viewed 3798 times


cordialement

Pierre

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Mon May 13, 2019 9:01 pm
by Peter Somogyi
Nice spectra gathered up here, especially the 15cm scope with 19 micron slit at high resolution!

However, my intention is using the 35 micron further (giving my 12"-scope access to RS CVn, CH Cyg and VV Cep in this region...).
Besides resolution, I suspect the S-index formula will be also dependent on the reference star + its curvature handling: e.g. just experienced despite Alf Boo is in the MILES database, but found its H & K wide features are poor for calibration, the response curve would be very unusual. It would be also nice to offer referene stars for each target (such that have no H & K widening).

Christian, the star HD 114519 is actually *the* RS CVn (= that I've just published before yours). Would it be possible using human readable names (or both), especially by which they are most commonly referred? It is hard to associate a 6-digit number to anything - at least for me, not sure about new visitors... Of course, only when have choice!

In fact, RS CVn looks as if missed the star (in fact didn't):
HD114519_PSO_compare.png

But the truth is, its period is 4.8d with eclipse duration 11% (not a rare event), so looking at our JD-OBS we both may have caught it in the eclipse.

The other interesting star worth to publish here on time, is Sig CrB = HD 146361:
SigCrB_PSO.png

Visually, looks there is some change.
However, I'm rather unsure what do we want to do with an S-index in case of these 2 stars (RS CVn has deep continuum changes, Sig CrB have interesting RV moves).

Next stars I've caught during same night: Ksi Boo = HD 131156, HD115404 (couldn't find better name), but these are similar to the already published ones.
Of course, I can upload them as soon as we have a db (question if want to correct for heliocentrics).

Peter

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Tue May 14, 2019 10:36 am
by Olivier GARDE
Last night, a first spectrum for me for this kind of target : HD 131156 (Ksi Boo) taken with my eShel spectrograph, but I don't refocus the spectrograph in the blue, so the resolution for #56 and #57 orders go down to R=6000.

Image

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Fri May 17, 2019 12:35 pm
by Alexandre Santerne
Dear all,

First of all, I would like to congratulate you for your enthusiasm in this project and especially your very high reactivity in performing outstanding observations, using impressively high-resolution spectrographs.

All of this is really encouraging and should be further explored. You have a lot of questions and I will try to answer them, but likely not in one message.

The emission peak in the core of the CaII H&K lines comes from the chromosphere of the star, that is heated by the magnetic field of the star. Therefore, this emission peak is one of the best proxy of the stellar activity. It was also observed for decades as part of the HK project at the Mount Wilson, which defined most of the metrics to use in this domain (such as the Sindex).

A few answers to your questions :

- The double-peak observed in the core of this CaII H&K lines is something normal in some stars. The Sun has such feature and is fully described in this quite-old publication http://adsabs.harvard.edu/full/1970PASP...82..169L (don't worry if you don't understand everything, me neither)
- The Sindex is important to measure so that observations can be compared between observers and instruments, in particular with the historical Mount Wilson surveys.
- A database is indeed the next step. There is one planned, but you are going too fast for me ;-) We can think on how to organise that.

So, getting such high quality spectra on the CaII H&K lines is a very good first step. The next step is to derive the Sindex for these stars are do time series over their rotation periods.

Here is an example of what we might expect for a moderately active star, in terms of Sindex variation. The plot below has 2 signatures, one periodic signal with a 18d period corresponding to the rotation of the star and a long-term trend indicating that the star undergo an evolution in his magnetic cycle.

Image

Long term variability of the CaII H&K emission is used to study the magnetic cycle of the stars. Here is an example on how we used it: https://arxiv.org/pdf/1107.5325.pdf

As described in the aforementioned paper, the Sindex is not the end of the story. The most used index is the logR'HK, which is based on the Sindex. The logR'HK is a kind of calibration to take into account the photospheric emission in order to compare the activity level of stars with different spectral type.
For instance, there was this study to link the chromospheric emission with the photometric variability: https://arxiv.org/pdf/astro-ph/0703408.pdf (see fig. 7).

So, it would be great to develop a pipeline that can extract the Sindex values out of your spectra and then to work on calibrating these values to derive the logR'HK which is the main scientific information.

Note that starting in July 18 this year, the spacecraft TESS will be observing the northern sky for about 1 year. There will be (bright) stars to observe (with long time series) in the CaII H&K domain in order to further understand the connexion between the photospheric features (spots / plages) and the chromospheric emission.

cheers,
Alex

PS: I have issue in displaying pictures... Here is the link : https://www.dropbox.com/s/lkwdg8h9uqykx ... n.jpg?dl=0

Re: Chromospheric active stars: a key program for amateurs

PostPosted: Sat May 18, 2019 7:44 am
by Olivier GARDE
Here's the picture...
Image