A few days ago, when doing some routine observations, I came upon a relatively bright star (13.5), that exhibited a very nice EW light curve.
A quick search in the VSX database to it’s current position didn’t shows any already known variable stars. So, at first sight, I thought I may have discovered an unknown variable. But a couple of hours later, I did a simple query on Simbad by position, which in fact, to my surprise, returned a name and some data for a star already catalogued in the Atlas catalogue (ATO).
Well well. That’s life.
Indeed, there are so many independent variable star catalogues by now, that may not be included in the VSX, it seems … So …
I was wondering what could be the most comprehensive process to be sure that a potentially new variable star is really what it is pretending to be : a new totally unknown variable star that can be included in the VSX.
Where to search ? In which catalogues having a close look, before claiming a discovery ?
VSX and Simbad (by position query) doesn’t seems to be enough, maybe ?
Hello, Christophe.
In fact, VSX and Simbad cannot guarantee whether something is unknown or not. We should also check Vizier (VizieR). Once you open the page, you can enter the coordinates in the lower left corner, select the appropriate Target dimension parameter, and then click “Go”.
Additionally, the FAQ and Guidelines on the VSX page can help you with some of your questions.
In fact, ATO entries need to be carefully reviewed. If they are labeled as “dubious,” feel free to boldly list yourself as the discoverer.
If Gaia or others have misclassified an object (such as classifying an EA as an S or an EA+BY as an RR), you can list yourself as a co-discoverer.
If a variable star is included in the Pan-STARRS1 RR Lyrae candidates in 2017AJ…153…204S and listed with an incorrect classification, you can add yourself as a co-discoverer (by the way, 2017AJ…153…204S has many problematic entries, making it an ideal place to search for new variable stars).
If the variable star is listed in The ZTF catalog of periodic variable stars (Chen+, 2020) - ZTF suspected variables catalog (Vizier:J/ApJS/249/18/table3), then it is also unknown.
If the variable star does not exist in any variable star catalog (such as Gaia, ATLAS, CSS, VSX, ZTF…), congratulations, it is likely an unknown variable star.
However, it is obvious that there are many related Vizier entries. When reviewing them, we need to carefully determine their meanings.
I hope this can help you.
Best regards,
Jiashuo Zhang
Thanks for this very useful answer.
I can effectively see that the Vizier webpage is listing a very broad set of catalogues for any given position or star.
That’s a good beginning.
I will also have a close look at the FAQ and Guidelines pages that you pointed to me.
It may be that I’ve found another pretty interesting EB in the TESS data. I don’t know much more on this star right now, but it seems it could be an unknown variable.
Incidentally, I have seen your communication on a similar subject on Cloudy Nights a few weeks ago : congrats for such a large number of discoveries !
I wrote a reply in this thread about your nice proposal for sharing some “secrets” ; most probably you did’t saw it
I submitted a very first variable star candidate about one week ago to the VSX, waiting for some news from the moderators.
As I have now a bunch of other candidates waiting “action”, I was working on assembling the mandatory elements to submit.
I have two more questions, if you don’t mind
One difficult point is to find the spectral type of the discovered VS. Historically, only bright stars had a spectral survey … but now, it seems that most of the variable candidates are faint. So where to find a spectral type for such faint stars ? I guess some spectras are lurking somewhere, deeply sleeping in some database …
Any help, idea or advice where to search would be welcome.
Another point is to do a phaseplot. Yeah … it’s pretty easy for most of the EB. But some stars have a regular pulsation only at first sight. When trying the assemble a phaseplot, one can see immediatly that this wouldn’t work properly.
What to do in such case ?
It is said, in the VSX Submission Manual, that you can’t only go with a LC that everyone can find on the web in databases…
Thanks in advance for any reply.
Cheeeeers,
Christophe
As to item 1: You can find spectra (but not spectral types) in the GAIA3 database (item i/355/spectra at VizieR). The faint limit there is G mag 15.0 (roughly Sloan r). If you have a list of targets of interest, I can classify them for you rather quickly, or tell you whether the spectrum is any good (not all are).
Regarding the first question, I will use an example of a variable star I discovered before.
I used Vizier and searched for the coordinates “02 10 52.49 +46 09 57.5”. Among the numerous entries that popped up, I looked for the entry “I/355/paramp”. Under this entry, you can see a “1” labeled in the Full column; clicking on it will redirect you to a new webpage. On this webpage, by searching for “spectraltype_esphs”, you can see that it gives a classification of type K. The classification information is on the far right.
(Although not all celestial bodies can be handled this way. Of course, sometimes LAMOST and SDSS can also provide possible spectral information.)
In addition, it seems that I misunderstood the second question to some extent. Are you referring to how to create a usable Phase Plot?
P.s. If Gaia spectra are used when submitting targets to VSX, it is necessary to cite the following references: Creevey, O. L.; et al., 2023, Gaia Data Release 3: Astrophysical parameters inference system (Apsis) I – methods and content overview, and 2023A&A…674A…26C.
hang in there.
The VSX submission queue has grown too large lately so we are still some stars away from your submission!
For faints sometimes there won’t be any spectral type. It is not mandatory to add one.
HI, Sebastian.
By the way, I sent you an email about Gaia DR3 variable stars a few days ago. I think you might have missed it due to your busy schedule.
Thanks for the tip and the proposition. This is great and very helpful.
I suppose I could send you a few Gaia spectra for identification, but doing this, I will never learn how to class those spectras. Also, as I suspect, I could find many new variables, I will always being dependant on you.
I have a better (but harder) way to try to class those spectras by myself, but doing this, I have a chance to become autonomous.
The first thing I have to do, I think, is to create an atlas of Gaia spectra by type A1 A2 … O, B, G and so on. Or search t find an ready made Gaia spectra atlas.
Thank you so much for this example, specially interesting. I will remember the advice.
About the phaseplot, I talk a few days ago …
The star I was thinking is almost periodic. One can do a phaseplot for a short period of time, this phaseplot will be correct for a few days. But looking further in the future, the period have changed, and the shape of the LC is slghtly different.
So, at first look, it seems periodic, but it is not.
In this case, should I paste the original LC as proof of variability, even it is available in the web, or should I provide something else ? What else ?
**
What is the STSP survey, often found in your submissions ?
Hi Christophe, perhaps you are using TESS data?
As far as I know, when using TESS data, one needs to consider contamination from nearby stars, among other factors, which may cause the light curve of a target to vary across different sectors, such as in the case of BD+21 2795. Perhaps you could attach one or more images to further illustrate the issue you are encountering.
Regarding the STSP designation, it is the main name I use when submitting variable stars.
I can assign my own designation to the variable stars I submit, such as ZJS V1, V2, V3, and so on. Of course, you can also choose your own designation.
STSP is the abbreviation for our group’s Stardust Transient Observation Project, which focuses on the search, photometry, and follow-up observational research of extragalactic novae and other celestial bodies.
If there is a GAIA (and LAMOST) spectral atlas rigged for MK type (rather than T_eff, log g, and [Fe/H]), then I would like to know about it. I have been doing this (for >10,000 stars) by building up a printed-out stack of templates of either MK standards or other reliable stars. I can send you the star-list, and perhaps you can work from those. Obviously simply comparing by eye is a low-tech way of doing this, but it takes a few seconds. But what I see in the literature when people try to do the classification with various software matching algorithms is they get the wrong type a lot.
Once again, an interesting link that the one you added to your last message.
The phaseplot for BD +21 2795 shows a regular period of 5.3028d, with various amplitude.
This is not the case about the star I found, which varies in amplitude, in shape, and in period.
This graph shows the LC for 3 sectors. In the first sector, p is about 4.7650d, in the second sector, p=4.8548d, and in the last sector, p=4.7530d.
So, adding the three sectors in one phaseplot is a very delicate task. Indeed impossible. Vstar can’t.
There are six sectors available in total, each with different period, shapes and amplitude.
In the last three sectors, the shape varies severely from the shape shown here. Some minima disappeard totally.
I checked for contamination, of course, but found nothing.
Thank you for the explanations about STSP.
Clear skies,
Christophe
Edit : I had a closer look to the phaseplot of the star BD +21 2795 ; it may be that the different minimas added in the plot does not coincide perfectly.
You did a 10000 spectra classification by yourself ? Whaou. That’s very impressive. What a task ! it’s the same number of spectra that were inspected by the Ladies in Harvard, for the first HD catalogue. Congrats and respects
Well, if I found something for MK types, I will let you know.
Of course, I’m interested in your list of stars.
Where can I get it ?
The light curves you attached are typical of a rotational variable. Spots migrate so the period doesn’t stay as constant as the period of an eclipsing variable or some strictly periodic pulsating stars. Also they may come and go so the mean magnitude and the amplitude change with time. In some extreme cases, spots almost disappear at times and the stars stay rather constant (around maximum, since a spotless star will be brighter).
Even then, you can get a mean rotational period by combining the different datasets. Don’t expect a “clean” light curve for these rotational variables.
The classification from ordinary GAIA spectra is pretty simple; I can tell most of them at a glance, so it goes very fast. It is not precise, but gets you +/- one-quarter or one-third letter type reliably, often better for late-type stars.
Below I’ll strip-in the list of star-names and types I’ve adopted. What I have done is to use the CDS VizieR display of the GAIA3 spectra, adjust the ‘normalized flux’ trace to fit the display, and then print them out — it is no more sophisticated than that. All the standards are unreddened (or nearly), and the profile changes due to interstellar reddening. The crude VizieR display needs a button to apply an ordinary reddening law (Cardelli et al) of varying amounts in reverse to get an unreddend spectrum to compare; there are surely smart ways to do this (machine-learning etc). Don’t expect a perfect match in every case, and there’s some slop in the comparison especially in the late-B to mid-F range.
H-alpha emission is visible when it is stronger than about 4A equivalent width; on some very young active stars you can see the “infrared” (far-red, really) CaII triplet in emission, and sometimes things like HeII emission in symbiotic stars, etc. Look at lots of odd cases to gain experience with this sort of thing (e.g. S-type stars, omitted here). Some nice examples of GAIA3 spectra for three new Wolf-Rayet stars are in a recent paper from one of our summer students last year:
…showing both the coarse GAIA spectra and new slit-spectra at classification dispersion.
…lots more canbe said about this sort thing.
GAIA3 spectra template stars
[BE74] 253 O8e non-std
ups Ori B0V MK std
HD 24131 B1V MK std
HD 36485 B2V MK std
HD 178849 B3V MK std
rho Aur B4V MK std
HD 161572 B5V MK std
HD 21071 B7V MK std
HD 66066 A B8V Garrison & Gray
HD 21931 B9V MK std in alf Per cluster
HD 66656 A0V MK std
HD 24805 A3V Garrison & Gray
HD 23585 F0V MK std
HD 27524 F5V MK std in Hyades
18 Sco G2V MK std
mu. Cas A G5V MK std, [Fe/H] = -0.8
HD 101501 G8V MK std
HD 185144 K0V MK std
HD 109011 K2V MK std
HD 219134 K3V MK std
HD 160964 K4V MK std
HD 190007 K5V Kirkpatrick std, maybe K4.5V ?
61 Cyg A K5V MK std
61 Cyg B K7V MK std
BD+27 1311 K7V Kirkpatrick std
LHS 164 K7V wl Jao et al
BD+33 1505 M0V Kirkpatrick std
HD 42581 M1V Kirkpatrick std
HD 33793 M1V wl MK std, given as M1VI; Kapteyn’s star
BD+01 2447 M2V Kirkpatrick std
Wolf 1061 M3V Kirkpatrick std
Stein 2051 A M4V Kirkpatrick std
GJ 1156 M5V Kirkpatrick std
Wolf 359 M6V Kirkpatrick std
vB 8 M7Ve Kirkpatrick std
vB 10 M8V Kirkpatrick std
HD 27022 G4III MK std
24 UMa G5II/IV MK std
HD 79698 G5III Keenan 1989
kap TrA G5Ib-II MK std
31 Aql G7IV MK std
HD 25877 G7II MK std
HD 147266 G8III MK std
HD 4404 G9.5II/III MK std
HD 63744 K0IIIb MK std
HR 5171 K0 0/Ia MK std
sig Hya K1III MK std
psi Boo K2III MK std
BM Sco K2Ib MK std, or lum class II
mu. Psc K3III MK std
HD 199697 K3.5III MK std, treated as K4III
nu.02 CrB K5III MK std
HD 196093/4 K5Ib non-std
HD 194193 K7III MK std
psi01 Aur K7Ib MK std
HD 38944 M0III MK std
75 Cyg M1III MK std
HD 163755 M1Ib MK std
HD 222670 M2III MK std
HD 10465 M2Ib MK std
HD 39045 M3III MK std
HD 27598 M4III Keenan 1989
HD 111499 M5-III MK std, treated as M5III
HD 12900 M6III Keenan 1989
BK Vir M7III MK std
RX Boo M8III MK std
CGCS 5973 carbon generic carbon star
HD 123821 C-R2+ III MK std, called C0,1 in the old scheme
CGCS 3636 C-Hd hydrogen-deficient carbon
UCAC2 F8kA2 CH UCAC2 41996644; carbon-ehanced, ex metal weak
UCAC2 G type carbon UCAC2 41878347
GJ 841 B DQ white dwarf with strong C2 bands
I begun to download the spectras. It is simple but efficient ; it seems it will do the job. It think I have a lot of work in front of me, but it is worth that.
Thanks for that list, and your nice replies.
The next task, now, will be to learn to submitt properly the new found variables, which will possibly be more difficult than expected.
I have a lot to learn, and many mistakes to avoid.
