Affiliation
American Association of Variable Star Observers (AAVSO)
Mon, 01/18/2016 - 00:50
The AAVSO PEP group is scrutinizing the stars we use for calibration. It would be nice if we could get spectra for the following star pairs:
Aqr: HD 129116, 129456
And: HD 10205, 10307
Per: HD 21551, 21552
Ori: HD 30544, 30545
These stars are all brighter than V=7.5. The Aquarius pair is of particular interest, and it is slipping away for the season. A single good spectrum of each star is all we need.
Tom
Is there a minimum spectral resolution you want for the spectra of those targets?
Having done no spectroscopy, myself, it is hard to quantify. What I am looking for are features that would complicate V and B band photometry - departures from smooth continuum.
A resolution (R = lambda/dlambda) of about 100-500 should be fine for what you want. That is about the resolution used for spectral classification as well as easilly doable with a filter-wheel grating (i.e. SA-200). Anything that doesn't show up at that resolution is probably not a worry for broad-band photometry.
I got the Perseus and Orion pairs tonight. How can I get those spectra to you?
You can download spectra of HD 10307 from Elodie database: http://atlas.obs-hp.fr/elodie/fE.cgi?ob=objname,dataset,imanum&c=o&o=HD%2010307
It is possible that something can be found from ESO archive, too.
Best wishes,
Tõnis
Hi Tom,
All these stars have multiple references to published spectral classifications so would be expected at least to have features typical of that spectral type.
http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/mk
Do you suspect that some of them might be peculiar in some way ?
Robin
Am I missing something? HD 129116 & 129456 are in Centaurus, not Aquarius. Are these the ones you are after?
Cheers -
Rob Kaufman (KBJ)
Hi,
I will take spectra from the stars of Andromeda, if clouds get away, of course. A resolution of 600 is enought?
Of course the spectra will be corrected from atmospheric extintion and instrumental response.
Greetings
Fran
Oops - yes those stars I labeled as Aqr are Centaurus. Those are also PEP calibrations stars, so no harm done.
The correct Aquarius pair is HD 210419, 210434
I can be reached at tee jay see at cantordust dot net. I have an ftp site that can be used for large files.
The problem we are having with the calibration star pairs (of which there are 12) is that some are giving wildly different values for epsilon V. This is the case for magnitudes based on either GCPD or Hipparcos. I'm running out of explanations, and it occured to me that spectral features might be a problem.
Maybe you want these monitored for awhile. I don't see a reason why they should change spectral flux. That would be entirely unexpected. But a simple experiment could try to rule it out.
What are the time scales that the epsilon V has shown variation on? Is it a case of two observers disagreeing on the same night? Or do you need to rule out that against all common sense one or both stars has unexpectedly changed?
The inconsistency is between eV derived from different star pairs measured by the same observer, usually on different nights. For instance, this past observing season, I got the following eVs for pairs in Andromeda, Hercules, and Aquarius: -0.024, -0.062, -0.013. Each is an average derived from two different nights. An eV determination based upon cluster IC 4665 gave a value of -0.045. Looking at our limited historical data, the Aquarius pair always seems too small. Aside from a pair in Pegasus, which Hipparcos showed to have significant magnitude variation, I don't (yet) have reason to suspect ongoing changes in the stars. There have been questions about the Aquarius pair going back to the 1980s.
It sounds to me like if (for example) the Aquarius pair is always low that there is a systematic at work in the photometry and purhaps the photometry of the stars relative to each other is in error. Have you checked them in APASS to see if there is a discrepancy between the "pubished" magnitudes and what they might really be?
It would be also interesting to know if eV is always low for a pair that are certain spectral types. Maybe the way the filter responses work an B4 V and a G8 (just making ones up) are always going to give a low eV when paired up.
I agree that something systematic is at work. With only a few exceptions, the PEP calibration stars are too bright for APASS. The stars are listed here: https://www.aavso.org/obtaining-your-pep-epsilonv-coefficient
There is no documentation for the sources of the magnitudes given there, and if you look at a much older calibration list, containing only four of these star pairs, you will see some magnitudes are slightly different. Below is a table showing eV for three stars pairs using V magnitudes and B-V indexes from the PEP web page, the General Catalog of Photometric Data, and the Hipparcos catalog.
PEP
GCPD
HIP
And
-0.024
-0.030
-0.039
Her
-0.062
-0.044
-0.055
Aqr
-0.013
-0.007
-0.054
Hipparcos certainly looks best in terms of consistency, but it doesn't match well with the cluster calibration of -0.045.
John has provided me with spectra for the Perseus and Orion pairs. Based upon past data, I expect Orion to give good results, and Perseus not-so-good results. The spectrum for the reddish Orion star is fairly well-behaved. But look at Perseus. There is a "notch" in the spectrum at about 510 nm. This is in the blue cutoff of the V band, at a high transmission fraction. Filters with slightly different roll-offs will sample this feature differently. Perseus also has a notch at about 620 nm, which is on the red cutoff of V band, though much further down the roll-off.
Still eagerly awaiting spectra for Andromeda and Aquarius, and if anyone can bear to stay up late (or get up early), the Leo Minor pair is HD 89904, 90040.
Hello,
I am currently taking the promised spectra. Just let me reduce them and tomorrow I will upload them.
Greetings
Fran
Hello,
finally I could reduce the spectra. Both have been corrected by iinstrumental response and extintion.
I hope they will be useful to you.
Greetings
Fran
Hello,
finally I could reduce the spectra. Both have been corrected by iinstrumental response and extintion.
I hope they will be useful to you.
Greetings
Fran