As one of my retirement goals, I am getting back into doing research. I tend to follow most recent novae, collaborating with Ulisse Munari to generate sequences and light curves. They don't take all of my research time, however.
What I would like to do over the next year is concentrate on anomalous cepheids, getting high precision photometry and spectroscopy of some of the brighter known or suspected candiates. These stars have been of interest to me for a long time, as they look like cepheids but are brighter than the typical cepheid of that period. The accepted theory is that these are merged binaries, so primarily happen in regions of high stellar density (globular clusters and dwarf spheroidal galaxies) and in late stages of stellar evolution. A good page of data is from the OGLE survey:
http://ogle.astrouw.edu.pl/atlas/anomalous_Cepheids.html
We've run a campaign on XZ Cet, which shows interesting behavior. I want to continue that campaign, but at 2hrs RA, it is only starting to appear in the eastern sky. Another prime candidate is BL Boo, which has the further value of being in the outer regions of NGC 5466, where there are several other variables. At 14hrs, it is a good choice for current photometry until XZ Cet gets higher. It gives you something to do in that "realm of the galaxies" region of sky!
BL Boo is at 14 05 40.47 +28 29 12.3 J2000, and ranges between 14.45 and 15.10 at V-band, with a period of 0.821301 days. There is essentially zero recent data on this variable in the AID, so placing it on your program will help fill in the gap. I'd much rather use data from the AAVSO community than take my own data! As with XZ Cet, I'll monitor the submissions and give advice on the photometry and spectroscopy forums. Spectroscopy? Sure - at 15th magnitude, it is difficult to do anything with a slit spectrograph on an amateur telescope with the necessary cadence (10-20 minutes), but I'd like to see someone prove me wrong. Perhaps more feasible is to use the SA200 diffraction gratings. At minimum, they will highlight any dramatic changes, such as the appearance of Halpha emission at a particular phase.
For photometry of BL Boo, please use either the 140 or 141 star as your comparison and the 146 star as the check. These have been carefully calibrated using the Sonoita telescope about a decade ago, when I did my last monitoring of BL Boo. Please transform your data, taking at minimum either B&V or V&Ic with every dataset. Unless you know what you are doing with ensemble transformation, use a single comparison star. You can follow the star all night long, take snapshots every hour or so, or even just one dataset per night. However, continue to monitor the star throughout its season, as I want long strings of data from each observer so that I can adjust any remaining offsets. Please expose long enough to get S/N > 100. One of the campaign goals is to show off the quality of multifilter data possible from the amateur community. Unfortunately, because of the desired precision, this is not a campaign for visual observers.
This first campaign can be started immediately. My intent is to write an initial paper after the end of the current observing season, so sometime late in the year.
Arne
I might add to Arne's comment the fairly obvious point that since observations of BL Boo go back several decades, new data will be useful for studying the long term period changes of an anomalous Cepheid. See, for example, the earlier study of BL Boo by McCarthy and Nemec:
http://adsabs.harvard.edu/abs/1997ApJ...482..203M
Period changes can be matched against the predictions of stellar evolution theory, and such period change studies are now available for few anomalous Cepheids. Gaps in observational coverage are often a problem in studying period changes, at least if the O-C method is used, so a wealth of new data on this important variable would be welcome from that standpoint.
Horace
However, are there any anomalous Cepheids of m>14 besides XZ CET?
Chris
Hi Chris,
If you consider that the anomalous cepheids are approximately the same absolute brightness, then distance scaling says that the only bright ones have to reside in our own galaxy. There are a couple of other candidates (such as TYC 1031-1262-1; look at Sipahi et al., 2013MNRAS.429..757S ) that I will suggest as we get farther into the project. Or, I bet Horace knows some good candidates!
Even having just one bright candidate should be enough to occupy a lot of telescope time for those that are aperture-challenged...
Arne
I just got back from a star prty and saw this thread.
I had many ACEP and ACEP candidates that I will never be able to publish so I think this campaign is a good way to study them.
I am adding them to VSX so by the end of the day you will be able to make a VSX search by type ACEP% and find them.
Cheers,
Sebastian
Hi Sebastian,
My first attempt at a VSX search for ACEPs yielded 47 records. Only 9 of these have AUIDs. I must have done something wrong....
Even so, I may pick one or two to load into VSTAR. I would assume that, among other things, we might be interested in getting good enough statistics to nail down more accurate periods for these candidates. Is that right?
Chris
See attached spreadsheet that contains the output I got from VSX yesterday. I got 59 records 16 of which have AUIDs. The ones that don't have AUIDs appear to be the CSS ACEPs that Sebastian just added.
UY Eri and DT Gem both are in uncrowded fields, are bright. and both have modern photometry, ASAS for UY Eri and Integral OMC data for DT Gem. I haven't found spectra, however. I don't know the best way to check for spectra other than searching SDSS and these are out of the SDSS fields. UY Eri has a somewhat bright(but significantly dimmer) nearby star but it is separated by about 12 arcsec which should allow sufficient separation. Perhaps if we had good candidates around the celestial sphere separated by say 3 hours. that would provide a continuous set of ACEPS to observe. Arne, what do you think?
Brad Walter, WBY
Hi Brad,
The CSS ACEPs were added back in 2014 by Patrick, I just added a couple now of those with AUIDs.
About UY Eri, this is an interesting case. I don't think it is an ACEP now.
There are a lot of contradicting publicatons in the literature about the classifications in the period range 0.8-2.4 d. and we need to sort things out eventually.
Now with the availability of sky surveys like ASAS or CRTS, this is becoming easier.
With Doug Welch we were checking several light curves and reading papers on RRAB/CWB/ACEP/DCEP and had an interesting discussion on these variables and their light curves.
I was (and I am) checking thousands of LCs and found that between ~0.8 and ~2.4 d. there is a mix of several type of pulsating variable stars but each has a different light curve shape and progression.
What the OGLE team calls fundamental mode ACEP (see their Atlas of variable Star Light Curves) is not recognized as such in other publications.
These are a neglected group of stars with no GCVS or VSX classification that has XX Vir as the prototype. They are called AHB1 stars in a 1996 paper by Diethelm but this 2006 paper by Sandage and Tammann is the key to this classification mess. AHB1 and ACEP (AC for them) stars are clearly separated because of their evolutionary status.
AHB1 (= XX Vir stars) are old Pop II stars evolving to the AGB after Helium core exhaustion and have low masses and higher luminosities (one magnitude brighter than RRAB stars). ACEP are brighter than AHB1 stars of the same period and fainter than classical cepheids. ACEP are more massive (~1.5-2 solar masses) while AHB1 are low mass stars (post-RR Lyrae).
These have the light curve shape of the RRAB stars with periods around 0.5 d. but at longer periods (0.8 - 2.4 d.)
Here are some prototype light curves:
XX Vir - AHB1 type, period 1.3482 d.
V0730 Her - RRAB type, period 0.4682 d. - Similar light curves
CSS_J100758.0+182825 - AHB1 type, period 0.812 d.
NSV 7806 - RRAB type, this is the actual light curve shape of a bona-fide RRAB star with a period of 0.805 d. and a hump in the ascending branch. Different from the CSS one which is AHB1.
The ones called ACEP in most of the literature are the first overtone ACEP in the OGLE atlas.
The AHB1 stars were classified as CWB in VSX (from the GCVS) because they had RRAB light curves but with periods longer than 1 d. thus not fitting the RRAB definition (but not because of a physical reason).
I reclassified them as RRAB in 2013 to separate them from CWB stars.
CWB-type light curves at short periods are like these:
UY CrB - 0.929 d.
BX Del - 1.092 d.
BL Her - 1.307 d.
See the bump in the descending branch going upwards with increasing period.
I didn't classify them as AHB1 or XX Vir stars because we didn't have that type in VSX at that moment. And we still don't have it now.
Back to UY Eri, it was classified as ACEP based on the OGLE classification but UY Eri is included in the above papers as an AHB1 star and its light curve shape indicates it is indeed in that same group of stars (I count 22 members of this class by now) as XX Vir.
If I were to revise it now I would call it XX Vir but since we need to add that type to VSX yet, I will hold on but tell you that don't include it in an ACEP project because it is different from the others.
John, about the ACEP type, we are following the class name most used in the literature.
If you check the VSX variability types document you'll find that ACEP is classed as a VSX type not because it is "new" but because it is not a GCVS type. They are called BLBOO in the GCVS after the prototype.
This also happens with other types, like the RR(B) type (RRD in VSX) or the LPB type (SPB for us and for the rest of the world).
Cheers,
Sebastian
Sebastian,
Where do I find spectra for these stars? Are there any large surveys that may have them or is it a matter of hunting for individual papers that have spectra included? Also are there any striking differences in spectra between ACEPS and AHB1stars? I would expect there would be since they are in very different stages of evolution.
Brad Walter
Hi Brad,
I don't know of a comprehensive source of spectra for these stars.
Most of the publications just mention their luminosities.
Actually both groups are metal-poor and have more or less the same temperatures and spectral types so it is the light curve shape which makes the difference (assymetric, RRAB-like for AHB1 stars and more sinusoidal, RRC-like for ACEP).
Their masses are very different too, 0.5-0.6 vs. 1.3-2.2 solar masses for AHB1 and ACEP respectively.
ACEP are probably the result of a binary merger.
Cheers,
Sebastian
Chris,
you didn't add the symbol % before and after ACEP.
This excludes all suspected ACEP since they are classified as ACEP: and also the EA+ACEP and ACEP+EA objects because searching by "ACEP" will only give you stars classified as such in VSX.
Cheers,
Sebastian
If you are not a MNRAS subscriber, try here for the paper on TYC 2011-1262-1
http://arxiv.org/pdf/1211.1200v1.pdf
Brad Walter, WBY
Arne,
How about observing in B and V, measuring with VPhot using both 140 and 141 as the ensemble (146 as check), and letting VPhot apply the transforms? Would this be an acceptable protocol?
Phil
Thanks for cleaning up the VSX entries, Sebastian! For now, I'd like to concentrate on BL Boo and XZ Cet. I'd rather get pristine light curves than dilute the pool. That said, I would not mind adding a couple of stars to the program, just as long as we don't try to cover everything possible all at once. Those that like data mining might go through the VSX list and find those stars that (a) are bright and in uncrowded fields, (b) have spectra, and (c) have both good modern light curves plus potentially some historical light curves. Post your results so a selection can be made. I've got some other duties for the next week or two, but will be monitoring progress.
Arne
Hi Phil,
The two-star ensemble with the 140/141 stars is ok, as long as these are going to be used for nightly snapshots and not time series. For time series, I'd really rather have a single comp star so that I can monitor (K-C) from the Extended Format submission.
Anyone who is going to submit nightly snapshots: I am going to request that you take a minimum of 3 sets of data, average them and report the mean and standard deviation. A program like Boxster can do this for you. I don't want to see single B,V measurement pairs, as that does not give me a good handle on the photometric error. Please don't submit the 3 individual sets, either - you need to do the calculation and not place that burden on me. If possible, put a note in the comments field indicating how many sets of data are averaged. If you do not take a minimum of 3 sets of images, your observation is less likely to get included in my analysis.
Note that this star has a period of about 20 hours, so taking longer than about 10 minutes for your nightly observation will result in some time-smearing of the light curve. This is ok, though I'd try very hard to get good signal noise and all images taken within, say, a half-hour. Then, if possible, add another note in the comments that indicates the time interval over which the observation was taken. Say that you take B1V1 B2V2 B3V3 and average them together, then the time interval to report is from the beginning of B1 to the end of V3. This results in a datapoint on the light curve that has two error bars: a magnitude one and a time one. The items I mention to add to the comments are not required, but are useful to me.
Arne
Note that TA can handle simple aggregations as well as the transforms. It will also put a note in the comment section documenting how many observations were averaged together prior to the application of the transforms.
George
I did a time series on BL Boo last night and calculated the TOM to be 2457134.7404 ( V mag of 14.457).
The exposure sequence was IRVBBVRI repeted 25 times with a cycle time of 22 minutes for the 8 images.
Analysis and transformation was done with LesvePhotometry. I'm not sure how Pierre arranges the groups with the above sequence but I will find out. Exposures of 120,100,120 and 180 for I,R,V and B gave S/N of ~80 to 110.
Richard Sabo
Hi All
Just posted a short run on BL Boo from the RC24 here on ACK. I don't have Tx Coef on that scope yet, but I took the images last night, before the BL Boo run. The sky crapped out and I had lots of images with clouds. So take the plotted data as a worst case. Seems like it aligned in all except B with SRIC.
Gary
Hello
Is anyone else getting the error: "# Duplicate label in chart. No CREFMAG available. Possibly bad chart reference Duplicate label in chart. No KREFMAG available." when using TA235?
I see no dupes and no standard chart. I am using an F" chart with 133, 140, 141, 1nd 146 from Sequence 14742BRV. I cannot transform obs from JD 7134. Have no others to try.
Had a similar error a week ago or so. We ignored it long enouh, and it went away. I emailed the files to George and it ran fine for him. THen it worked for me.
Arne, anything special about the VSP files for this star?
Gary
I replaced the time series of 2457134. The images were acquired in groups of eight - IRVBBVRI - but that did not fit the requirement of LesvePhotometry. I stacked paired images from IRVBBVRI into groups of BVRI and reanalyzed the run. Better S/N and a better curve.
Richard Sabo
Hello All
I am on the earlier learning curve here but I have a question about the "ACEP" variable type you are speaking of.
I did the VSX search and got the 57 objects and ten for "kicks" I did a search of my GCVS and the new GCVS4 databases for the ACEP type and got no hits at all. I went to "Observing Variable Stars" by Gerry A Good and could not find that designation listed there either.
Is this only a type within AAVSO or have I miss something here.
John (RIZ)
Hello Arne
Since there are two 140's and two 141's, I just want to confirm which we are to use. I did the RA and DEC comparisons, but want to get a final ck. the 140 is AUID 000-BKP-271. I would use this as my comp--single star. For ref, the 141 is AUID 000-BKP-269?
Gary
Sebastian
Thanks for the explaination. I did find the VSX document you mentioned shortly after I posted my question and found the ACEP description there and better understand what you all are working on now.
Thanks again
John
Gary, if you do the standard 30arcmin plot from the "pick a star" window on the home page, there are only one 140 and 141 star, BKP 269 and 270. They are located about 5arcmin to the west. I don't know anything about a BKP-271. I also tried a 15-minute scale, and the F-scale, and there was no duplication. My guess is that somehow you are picking up old/deleted sequence stars, but I don't know how you would have gotten into that state!
Arne
Hi Arne
Thanks for confirming that BKP-269 is the 141 and BKP-270 is the 140. That will prevent a boatload of errors getting into AID and then having to delete them, which is not easy.
Its not only me that got old values if that is it, TA, when it querries the data base is making the same mistake, and then it does not Transform--gives the error message, etc etc.
Try putting in the sequence from VSP, not the pick a star window on the home page, and enter 14766CR as the photometry report, and you will get 6 stars, and 2 dupes for 141 and 140. That is how I got them. I will look at the home page as see what I get there.
How did I get 14766CR, well I first got a chart of BL Boo, then asked for the PT table, got 4 stars and the ref seq as 14766CR. When I entered that at a later time, I got the 6 stars and two dupes.
Gary
Hello Arne and All
I tried to get a PT chart by first entering the name BL Boo on the front page. Got a 1 degree chart. Then clicked Return and Replot. Asked for a PT chart. Got one with only dupes for the 107--which showed up on the 1 degree chart, and a ref of 14771CSP for the photometry.
Then went back to VSP and entered 14771CSP for the chart name (BL Boo was left as the star name) and the resulting PT Table had dupes for 107 (as it should) and 140 and 141 (which is new). If I remove BL Boo from the star name, I get the same PT Chart with 3 dupes--ie no effect.
This becomes a problem when Transforming the data, as TA now will not complete the transformation.
Hope this helps
Gary
Just so you don't think you are going crazy Gary, I'm having the same problems and they come and go. I was able to duplicate your Dupe problem. I was also unable to get the size of chart that I wanted. I was also unable to get to any photometry table and finally the chart page wouldn't even give me the option of opening the photometry table from the chart page. Pretty much a train wreck.
This was using Firefox. I changed to Chrome and got what I needed.
Jim jones
Hello Jim
Glad to hear that you can verify the VSP issues. I suspect that Will is working on things, and that may be why the results are a little inconsistant. FYI, I was using both Firefox and Chrome.
One thing that surprised me, and it may be a clue, everytime I ask for a Photometry Table, I get a new Reference Label, ie xxxxxxABC, and it changes everytime, and its not the same, even if the field is the same. Not sure it should do that, but it does.
Gary
If I recall correctly when I investigated this about a year ago with Sebastian, the answer I got was that if there is any change to the database (not sure if that is just AID, or AID and VSX) between your two identical requests, even though it has nothing to do with the star or the field you are requesting, you will get a new number. I think the same thing is true for the finder chart as well. I just requested exactly the same BL Boo 30' VSP finder chart with exactly the same settings 2 minutes apart and the finder chart IDs were different. 14773KZ and 14773LA. I can't remember in recent years ever getting the same ID twice for chart or PT requests with identical settings no matter how closely spaced the requests were.
Brad Walter, WBY
Hi Brad et al.,
Every time you make a chart or photometry table request you will get a new code, it doesn't matter if you enter the same parameters.
The use of the code is meant to avoid the need to enter the same parameters again. You just use the code and get the same chart, not the other way around (entering the same parameters and expecting the same code to show up).
In short, if you want the same chart you should enter the code you got at your first try.
Cheers,
Sebastian
Why on request %ACEP% I can not get a list of.
Are you entering %ACEP% in the "Variability Type" box near the bottom of the page after clicking "More" twice? I just did it and everything worked fine.
Brad Walter, WBY
Not
Understood. Thank you.
Not all the stars in the VSP have chart. How to be in this case?
Nikolay
All Stars in VSP (Variable Star Plotter) do have charts. I think you mean that all stars in VSX don't have charts. That is true.
VSX is a very comprehensive index of variable stars, many of which do not have observations submitted to AAVSO. It simply takes too much time and effort to make charts for variable stars that no one is observing. Someone needs to request a sequence to be made and loaded for the star for VSP to generate a chart, and before a sequence can be loaded, the star must also have an AUID (AAVSO Unique ID). Most stars in VSX have AUIDs but on occasion I have found one that doesn't. The URL below covers all of the processes for requesting a new chart sequence to be made. The process is simple and fast.
However, sometimes a chart has been prepared but you are using a name that VSP doesn't recgonize.See the attached document I put together for last VStar session about names to use when accessing Data in the AAVSO International database which applies to names for VSP as well.
Also look here: http://www.aavso.org/request-comparison-stars-variable-star-charts .
The sequence team
Hi Nikolay
The sequence team tries hard to make sure that stars that are in VSX and that people are observing or will observe have charts (sequences). In many cases the team generates sequences for new variables in the expectation that they will be observed. Sometimes they even generate a sequence for a star that isn't in VSX yet.
In my experience, there can be several reasons that a star that is in VSX doesn't have a chart.
1. For various reasons the star simply isn't a star that is being observed. For example it may be a star that was reported in the literature to be variable but is in fact constant.
2. There simply may not be any stars in the field that we can use for a sequence. This is rare but it happens.
3. The team isn't aware of the need for a sequence.
If you want to observe a star that doesn't have a chart you can find help at
http://www.aavso.org/request-comparison-stars-variable-star-charts
If you make a request you will frequently get a chart within hours. Very rarely the team will get a request that can't be filled, but that is rare indeed.
Jim Jones
Arne said:-
"Spectroscopy? Sure - at 15th magnitude, it is difficult to do anything with a slit spectrograph on an amateur telescope with the necessary cadence (10-20 minutes), but I'd like to see someone prove me wrong."
Hi Arne
Could be tough even for the Star Analyser but it sounds like a potential target for my modified "ALPY 200" slit spectrograph. Designed for ~50A (Star Analyser like) resolution but the slit keeps the sky background out so can go fainter (reaching mag 17.5 in 2hrs with 280mm aperture on supernovae currently so mag 15 in 20 min could be within range) More info here
http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm
http://www.threehillsobservatory.co.uk/astro/spectra_46.htm
Robin
BL Boo appears to be changing very rapidly.
With my system (LX200 12", f/5.6, ST7) it takes almost 25 minutes for a BVI image set with centimag precision. When I go to aggregate a series of 5 BVI's the error is upto 0.04 because the 5 images are clearly trending, not a scatter.
Could you clarify the requirement for aggregating data for this project? Maybe a maximum time span for aggregated data. Or maybe a minimum time span for a image set; maybe I'm playing in the wrong game.
George
Hi George,
With a period of 0.821days, that is 1183 minutes. My usual rule of thumb when imaging pulsating stars is to get 100 phase points, or a point every 11.8 minutes. So a cadence in the 10-20 minute range will normally be ok. That said, there are phases when the variation may be faster, such as the rapid rise of an RR Lyr star to maximum, or resolving the flux peak. I think you are saying that you are getting ~0.01mag precision per data set, so there is no strong reason to average 5 such sets together and blurring your cadence. This is one of those cases where I'd average fewer sets (say, 3), or even report individual sets since there is significant variation between sets with your telescope.
Arne
Where to send the results of observations. For example H1135 Her is not possible to upload AAVSO?
Given below is a phased plot for BL Boo, taken from VStar (thanks, David!). Seven observers have contributed data. Gary, I think your observations have come from multiple telescopes as well, including some AAVSOnet ones.
In general, we've gotten excellent phase coverage of this star for this season, except at minimum. If you do nothing else, try to concentrate there and get a bit more data.
Now the details. The RMS of the curve is great, about 0.02-0.03mag, considering the number of systems. The biggest scatter is where the photometric error is largest, a nice confirmation that the error treatment is correct. The epoch has obviously shifted from that given in VSX; perhaps someone can recalculate this and submit it as an update via VSX.
Gary has a bright V-band measure with TMO61 on 2457162.635 that is shown with minimal error, but about 0.1mag too bright. He also has a faint V-band measure at 2457167.56 about 0.15mag too faint. There appear to be a bit more offset between observers in the B-band. In particular, the cluster of observations at phase 0.05 from MNIC seem bright by 0.1mag. They are not listed as transformed. You can go through and pick out a few other isolated datapoints that should be examined by their respective observer. The major point here is that these points lie ~ 3sigma off the curve, enough to be suspicious that an easily-found error can be identified, but not so far as to be statistically improper.
The one enticing feature is some possible structure near minimum. However, we don't have enough high-quality data there to be sure.
I'd spend another night or two on this object, and then we can move over to XZ Cet, which should be doable by everyone now in the morning sky. Anyone try some diffraction grating spectra of BL Boo? Anyone look for other variables in this field?
Arne
Arne:
I ran untransformed time series photometry for all the other valid (VSX) variables in my BL Boo FOV and reported the data to AID (1636 data points). Variables show significant magnitude ranges. Will probably play with them in VStar to check periods?
It would be nice if the other six observers could enter their data too. VPhot does it easily.
Edited 150704: I generated time series for all the other variables and provided the VPhot Time Series summary table (below) the first time I wrote this post. Then I looked at the data and saw something I did not believe. Comp 146 shows some variability (see range)?? So I deleted the table. I'm thinking about it some more but got brave enough to put the table back in. It would be interesting to know if anyone else saw any variation of 146 of a similar magnitude range (14.3 - 14.7) over many days (not hours). If not, it makes me suspicious of the other data although many others look like normal RR Lyr star plots and match with VSX type designation.
Help?
Ken
Ken,
I have 8 nights' data on this field and using 140 and 141 as comp stars I find a mean transformed V mag for 146 of 14.571 with std dev 0.017.
David
David:
Yes, I also got a mean near the expected value and std of 0.03 but got a max/min range of much more, as seen in the table provided. It was strange? Thinking some more, it didn't look like one bad outlier when I looked at the graph for this check but I guess it was! That must be what explains the tabulated wide max/min range? Occam's razor!
Ken