Photometric AAVSO also for B and Rc

[achim2205]

Hello Han, I like using the tools for variable star annotation and quick creating the AAVSO report. V and B values are shown in the annotation. But how to work with B instead of V? And what about Rc? Rc is also listed in the AAVSO database.
Regards Achim

[han.k]

Yes that is possible. The formulas for calculating these magnitudes from Gaia are documented.

There are three options. I put all these magnitude in one database, split it in separate databases or put the Gaia magnitudes in a database and calculate them on the spot.

I will look into it.

Today the V17 Johnson-V database will be replaced by the V50. No difference in magnitudes except it is based on Gaia DR3 and not eDR3. This one will work universal for both solving and photometry and because it is in the 1476 format it will be a little faster.

Han

[han.k]

I looked into it. I think the best way forward is to create a new database with the three original Gaia magnitudes. From these three it possible to calculate later any filter band magnitude.

For photometry it also better to sort it on magnitude rather then star density. Then it will be complete. So you will get a V17 or V18 on steroids.

You will need also the corresponding filters or use a colour sensor.

[achim2205]

My latest photos from SNs are in Johnson V and B and Cousins R. So it will need a selection in the photometry tab to select the used filter.

[han.k]

I'm doing remote astronomy with B/W-cameras spread worldwide having Johnson B and V and Cousins R-filters (and also the standard L, Ha, S2, OIII ... filters)

I think now the best approach for this is to access Gaia online. That is already available. This will give in 10 seconds or less the 3 Gaia magnitudes of all stars in the image. From this the other magnitudes can be calculated as documented in Gaia documentation. Then the program can scroll through the images. I can then also access other things like the flag like "disturbed".

In the photometry tab adding drop down combobox with the follow options:

• local database V
• Online Gaia -> Johnson-Cousin V
• Online Gaia -> Johnson-Cousin B
• Online Gaia -> Johnson-Cousin R
• ....
• ....

Saves me also creating an other database.

The relations are here documented:
https://gea.esac.esa.int/archive/documentation/GEDR3/Data_processing/chap_cu5pho/cu5pho_sec_photSystem/cu5pho_ssec_photRelations.html

[achim2205]

The relationship between Gaia, Johnson/Cousins and Sloan G / R (magnitudes of SNs in ZTF observations) is well known to me, I convert those using an Excel table.

What I like is shown in the example: Just switch between the filters and seconds later, we'll get one by one the AAVSO-report for V , B or Rc - of course loading in between another filter image
Regards Achim

[han.k]

I'm making progress. I can't find a direct relation between Gaia magnitudes and Rc. Do you have this worked out?

[han.k]

Correction B is missing, Rc must be R. Maybe B can't be predicted correctly with Gaia filters.

[han.k]

For Rfollowing remark J it is only valid for:

2.0<GBP−GRP<4.0

[han.k]

The closest transformation available is Tycho Bt or SDSS g

Note (G1): Central wavelengths and their FWHM are (in nm, from table 1):
    ±---------------±------------------±-------------------±-----------+
    |      Gaia      | Johnson-Cousins   |       SDSS         | Hipparcos  |
    | G  Gbp Grp Grvs| U  B    V   R   I |  u   g   r   i   z | Hp  Bt  Vt |
    |----------------±------------------±-------------------±-----------+
    |673 532 797 860 |361 441 551 647 806| 357 475 620 752 899| 528 420 532|
    |440 253 296  28 | 64  95  85 157 154|  57 118 113  68 100| 222  71  98|
    ±---------------±------------------±-------------------±-----------+

[achim2205]

from Gaia you'll need G / Bp / Rp and (B-V)
then I use attached formulas

R is Rc, due to 'c' stands for Cousins. Johnson only created U / B / V.

[achim2205]

another way:
- leave V as it is in V17
- use B and Rc values from those stars, which are listed in AAVSO
Regards Achim

[han.k]

The first three lines are a filter.

I can transform from Gaia to the V and R magnitudes, B is missing. If you say:

R:=V-0,506x(B-V)-0,004
then
B:=V+ ((R-V+0,004)/-0.506)

Where does this relation come from? Did you curve fit this?

is it not better to adapt the Bt relationship because it is close to Johnson-B with curve fitting?

[achim2205]

Here I found the R formula
http://www.aerith.net/astro/color_conversion.html

[han.k]

Okay.

An other possibility is first to calculate Tycho Bt and Vt and from those two then B by

B - V = 0.850 * (BT - VT)

Should give the same result. I wil try this later in the afternoon and compare some results.

[han.k]

I prefer the transfromation form Bt and Vt since Bt is very close to B.

Looks all okay. Here are the transformations. Tell me if I make any mistake:

      begin //transformations
        if ((G>0) and (BP>0) and (RP>0)) then //transformation is possible
        begin
          BminR:=Bp-Rp;
          if magn_type='V' then
          begin
            if ((BminR>=-0.5) and (BminR<=5.0)) then {formula valid edr3, about 99% of stars}
            begin
              V:=G + 0.02704 - 0.0124*(BminR) + 0.2156*sqr(BminR) -0.01426*sqr(BminR)*(BminR) ;  {edr3}
              mag:=inttostr(round(V*10));
            end;
          end
          else
          if magn_type='B' then
          begin
            if ((BminR>-0.3) and (BminR<3.0)) then
            begin
              Vt:=G + 0.01077 + 0.0682*(BminR) + 0.2387*sqr(BminR) -0.02342*sqr(BminR)*(BminR) ;
              Bt:=G + 0.004288 + 0.8547*(BminR) -0.1244*sqr(BminR)+ 0.9085*sqr(BminR)*(BminR) - 0.4843*sqr(sqr(BminR))+ 0.06814*sqr(sqr(BminR))*BminR ;
              V:=G + 0.02704 - 0.0124*(BminR) + 0.2156*sqr(BminR) -0.01426*sqr(BminR)*(BminR) ;
              //B - V = 0.850 * (BT - VT)
              B:=0.850 * (Bt-Vt)+V; //from Tycho catalog
              mag:=inttostr(round(B*10));
            end;
          end
          else
          if magn_type='R' then
          begin
            if ((BminR>2 {remark J}) and (BminR<4.0)) then
            begin
              R:=G + 0.02275 - 0.3961*(BminR) + 0.1243*sqr(BminR)+ 0.01396*sqr(BminR)*(BminR) - 0.003775*sqr(sqr(BminR)) ;  {edr3}
              mag:=inttostr(round(R*10));
            end;
          end;
        end;//transformation is possible

[achim2205]

Hi Han, I tested the formulas used above, see attached Excel-table.

[han.k]

Some differences. Not all the stars perfect. More testing is required. See remark 1) and screenshot.

Try now this development version:
http://www.hnsky.org/astap_setup.exe

1) You can plot the transformed magnitude of Gaia in R, V and B
2) Rc is added to the online VSP annotation
3) Photometry should work for R, V, B

Now it has to be tested. Do you have some images for me made with a R, V and B filter? Then I can test the measurement of the AAVSO VSP stars.

I have also relaxed the formula for Rc (ignored remark J because too many stars where excluded):

           if magn_type='R' then
              begin
                if ((BminR>0 {{remark J, could be 0.2}) and (BminR<4.0)) then
                begin
                  R:=G + 0.02275 - 0.3961*(BminR) + 0.1243*sqr(BminR)+ 0.01396*sqr(BminR)*(BminR) - 0.003775*sqr(sqr(BminR)) ;  {edr3}
                  mag:=inttostr(round(R*10));
                end;
              end;

See attached screenshot

[han.k]

Is there a need to call red Rc or is R sufficient?

[han.k]

Gaia online is currently a little slow. Could take 20 seconds

[achim2205]

R is OK.
I made some more test calculations, see attachments.
Where can I upload the BVR-files?
Regards Achim

[achim2205]

the files are at https://ufile.io/0olvawap

[han.k]

You could upload to
https://ufile.io/
but zip the files first in one file and share the link .

[achim2205]

see my last post

[han.k]

I got the images. Good test material.

I will allow measuring B and Rc magnitudes at the mouse pointer. That is missing.