It depends upon the sequence that has been pre- built by a sequence team member and placed in the VSD data base, which is where the VSP selects it's data from.. This action depends upon what Survey data is available, what the filter options are and what the V range is. In addition, sometimes, even when there might be data available from a specific survey, as a first choice, we may have reason to question it's accuracy and or completeness based upon what we observe in the data and then may have to move to a second option.
Typically, in recent years, APASS data is used for the ~ 10V - 16.54 V range with either SDSS ( ~14.8V-18.7V) or Pan-STARRS (~14.5 - 19.5V) being the most used for fainter targets.
APASS is by far, at the moment, the most comprehensive survey available in terms of sky coverage.
If Henden Data is available it is always golden and a great first choice (~13V - 18.7V) Also SRO data is really good if available ~ 10.3 - 17V.
Sometimes we use CMC15 data (~10V - 14.4V).
For the Brighter targets we have a choice of three surveys: BSM (~6.3V-13V); GCPD (~.01-6.5V) & Tycho-2 (~ 6.5V - 10.2V).
Occasionally, there are probably a few obscure surveys that are used only when no other option.
In addition, there is still some original data from the first population of the VSD, at the VSP's inception that may come from other sources as the best then available.
I hope this answers your question. If you need further info on this process feel free to email me directly: tcarchcape@yahoo.com.
Thanks Tim. I was unclear in my question. I was actually after the non-variable, non comp stars, but I am also interested in the catalogs you use for sequences, so thank you very much for that information. I will contact you by email for more information about the comp sequence sources.
Phil, are you talking about the stars that are plotted on the chart, or the comp stars? Tim has given you all of the information regarding where the comp star data comes from. Just to complete the picture, the stars that get plotted on the charts (other than the photographic DSS) come from three sources:
- brightest stars are from Tycho2
- intermediate-bright stars are from UCAC4
- faintest stars come from USNO-A2.0
Those were the best sources when VSP was written. It would be possible to do everything using GAIA stars today, but that means a rewrite of the search engine, which takes programming time that is not available/prioritized. One of the neat things about using GAIA is that, with its proper motion information, you could generate the chart for any date that you want. A high proper-motion object like Barnard's Star would then be plotted where it is tonight, not where it was recorded in 1985.
I downloaded a chart for BZ Cam with chart scale F (18.5 arc min) on 2018-12-03. It shows labeled comparisons from 116 to 155. Downloading a CCD photometry table just now claims there are no comparisons in the database. Sure enough, downloading the chart again and labels are nowhere to be seen.
More on this one. My system runs Ubuntu 18.04LTS and has Chromium "Version 71.0.3578.80 (Official Build) Built on Ubuntu , running on Ubuntu 18.04 (64-bit)" and Firefox "64.0+build3-0ubuntu0.18.04.1".
Comparison stars are available to Firefux but not Chromium. I've been unable to find any change of setting to Chromium which lets it work.
If a web developer wouild like to investigate I'll be happy to help. Until then I have a workaround.
Make sure that the VSP chart option "Would you like a special field?", found at the bottom of the chart Advanced Options, is set to "none" and not "Standard Field".
Phil,
It depends upon the sequence that has been pre- built by a sequence team member and placed in the VSD data base, which is where the VSP selects it's data from.. This action depends upon what Survey data is available, what the filter options are and what the V range is. In addition, sometimes, even when there might be data available from a specific survey, as a first choice, we may have reason to question it's accuracy and or completeness based upon what we observe in the data and then may have to move to a second option.
Typically, in recent years, APASS data is used for the ~ 10V - 16.54 V range with either SDSS ( ~14.8V-18.7V) or Pan-STARRS (~14.5 - 19.5V) being the most used for fainter targets.
APASS is by far, at the moment, the most comprehensive survey available in terms of sky coverage.
If Henden Data is available it is always golden and a great first choice (~13V - 18.7V) Also SRO data is really good if available ~ 10.3 - 17V.
Sometimes we use CMC15 data (~10V - 14.4V).
For the Brighter targets we have a choice of three surveys: BSM (~6.3V-13V); GCPD (~.01-6.5V) & Tycho-2 (~ 6.5V - 10.2V).
Occasionally, there are probably a few obscure surveys that are used only when no other option.
In addition, there is still some original data from the first population of the VSD, at the VSP's inception that may come from other sources as the best then available.
I hope this answers your question. If you need further info on this process feel free to email me directly: tcarchcape@yahoo.com.
Tim Crawford, Sequence Team
Thanks Tim. I was unclear in my question. I was actually after the non-variable, non comp stars, but I am also interested in the catalogs you use for sequences, so thank you very much for that information. I will contact you by email for more information about the comp sequence sources.
Phil
Phil, are you talking about the stars that are plotted on the chart, or the comp stars? Tim has given you all of the information regarding where the comp star data comes from. Just to complete the picture, the stars that get plotted on the charts (other than the photographic DSS) come from three sources:
- brightest stars are from Tycho2
- intermediate-bright stars are from UCAC4
- faintest stars come from USNO-A2.0
Those were the best sources when VSP was written. It would be possible to do everything using GAIA stars today, but that means a rewrite of the search engine, which takes programming time that is not available/prioritized. One of the neat things about using GAIA is that, with its proper motion information, you could generate the chart for any date that you want. A high proper-motion object like Barnard's Star would then be plotted where it is tonight, not where it was recorded in 1985.
Arne
Thanks, Arne. That's what I wanted to know.
Phil
I downloaded a chart for BZ Cam with chart scale F (18.5 arc min) on 2018-12-03. It shows labeled comparisons from 116 to 155. Downloading a CCD photometry table just now claims there are no comparisons in the database. Sure enough, downloading the chart again and labels are nowhere to be seen.
What gives?
Paul
Hmm, Looks like a generic problem. LS Cam gives the same (lack of) results.
Ho hum. I'll wait until tomorrow and see whether it's fixed then
Another Heisenbug.
Now works fine.
Something is playing with my paranoia. "Infamy! Infamy! They've all got it in for me!"
More on this one. My system runs Ubuntu 18.04LTS and has Chromium "Version 71.0.3578.80 (Official Build) Built on Ubuntu , running on Ubuntu 18.04 (64-bit)" and Firefox "64.0+build3-0ubuntu0.18.04.1".
Comparison stars are available to Firefux but not Chromium. I've been unable to find any change of setting to Chromium which lets it work.
If a web developer wouild like to investigate I'll be happy to help. Until then I have a workaround.
Make sure that the VSP chart option "Would you like a special field?", found at the bottom of the chart Advanced Options, is set to "none" and not "Standard Field".
That was it, thank you.
I'll try to remember that next time.