Return to the Cloudy Nights Telescope Reviews home page


Observing >> Double Star Observing

Pages: 1 | 2 | (show all)
GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: STF450 - in search of evidence new [Re: fred1871]
      #6273058 - 12/26/13 02:41 AM

It's worth noting that the completeness limit in the Hipparcos catalog is dependent on galactic latitude. The mission was designed to retain a fairly consistent density on the sky of about 4 stars per square degree. And so the completeness limit is about 9m at the poles (toward CrB and Scl), rising to about 7.5m at the galactic equator. That M45 is at about latitude -20 degrees suggests a completeness nearer to 8m, meaning that the star in question will not have appeared in the HIP input catalog (HIC) unless it's a special program star, some number of which were included to as faint as about 12m.

Post Extras: Print Post   Remind Me!   Notify Moderator  
WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: STF450 - in search of evidence new [Re: GlennLeDrew]
      #6273162 - 12/26/13 06:55 AM Attachment (10 downloads)

Glenn - thanks, I have often wondered why rather bright stars are not Hipparco listed while rather faint ones are very well, this explains it.

Fred - thanks for the explanation regarding USNO A2 magnitudes. I don't know the spectral type of USNOA2 1125-01267467 (I have the catalog on DVD at home but have at this moment no access to it) but your assumptions seem plausible.

Regarding TML for a 60mm refractor: I know that there are so many factors involved that any given number can only be a mean value with some range for deviations - but I think somewhat slightly above +11mag should be possible.

Meanwhile I checked again the photo of Chris for another reference and found also nearby HD 282973 +9.87magV according to Simbad resp. UCAC4-570-008510 +9.98mag.
To make a direkt comparison I arranged STF450A, STF450B, UCAC4-570-008469 and UCAC4-570-008469 side by side - this shows clearly that STF450B is in between UCAC4-570-008469 +10.84mag and UCAC4-570-008469 +9.98mag and certainly fainter than the latter.
Wilfried


Post Extras: Print Post   Remind Me!   Notify Moderator  
freestar8n
Post Laureate
*****

Reged: 10/12/07

Re: STF450 - in search of evidence new [Re: WRAK]
      #6326229 - 01/21/14 01:50 PM Attachment (5 downloads)

Hi-

I don't post here much and I don't do much double star work, but WRAK asked about this double in a photometry thread and I thought it might be interesting to look at it. So I took some video with an Edge8 and qhy5l-ii using C, g', and r' filters (Sloan). I did not have much time so I did not do an elaborate calibration or anything - and this is all raw measurement - but I think it tells the story. Basically the third star is very red, with a color index of 1.65 according to one source (described in a later note below).

Here are stacked images with no processing other than aligning and sub-sampling - and dark subtract. These are stacks of 200 frames at 100ms exposure with no quality culling. The star was lower than I wanted and I believe the atmospheric dispersion in the longer filters causes the elongation - it is not a collimation issue.

So here are the images in clear, g', and r' all at the same scale. They are *not* corrected for extinction or response of the camera, but they tell the main story - the third star is very red.

Frank


Post Extras: Print Post   Remind Me!   Notify Moderator  
freestar8n
Post Laureate
*****

Reged: 10/12/07

Re: STF450 - in search of evidence new [Re: freestar8n]
      #6326241 - 01/21/14 01:55 PM Attachment (6 downloads)

Here is a spreadsheet of the measured flux in the stars along with their positions. I did not calibrate the pixel scale so it is based on an assumption of 3.75 micron pixels and 2000mm fl, with sub-sampling by a factor of 4 - which is about 0.1" per pixel in the measured system shown.

I calculate raw magnitudes and then adjust them relative to the g' value for the primary and its color index from below. This is not intended to be exact but it gives the idea of the relative colors of the stars.

Frank


Post Extras: Print Post   Remind Me!   Notify Moderator  
freestar8n
Post Laureate
*****

Reged: 10/12/07

Re: STF450 - in search of evidence new [Re: freestar8n]
      #6326248 - 01/21/14 01:58 PM Attachment (10 downloads)

And here, which somewhat takes the fun out of it, is a Vizier search of the region, which comes up with a database hit of photometry on the Pleiades stars, including STF450. It gives a color index of 1.65 for the fainter star, which is very red.

I don't know how the mags are assigned or adjusted for visual observers or in the double star lists - but this is more information to go by, including captured images. It's a very red star - so it may not match the listed magnitude - depending on how it's measured.

Frank


Post Extras: Print Post   Remind Me!   Notify Moderator  
WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: STF450 - in search of evidence new [Re: freestar8n]
      #6326601 - 01/21/14 05:27 PM

Frank, thanks for the effort you invested here - I am not sure how to read all these numbers but I tend to the interpretation that the STF450 companion is fainter than WDS advertised +9.1mag.
Wilfried


Post Extras: Print Post   Remind Me!   Notify Moderator  
freestar8n
Post Laureate
*****

Reged: 10/12/07

Re: STF450 - in search of evidence new [Re: WRAK]
      #6326754 - 01/21/14 06:41 PM

I'm mainly pointing out how the third star itself is very red, and the second one is fairly red. The values from Eichorn's study in 1970 are 7.22 9.65 10.71, with color indices -0.01, 0.71, 1.65.

My images show the third star almost disappearing in the g' blue-green filter that is close to V, while it is much brighter in the red r' filter. The second star has the same behavior but less so.

I don't know how accurate the Struve values are or if he was skewed by red in the color - but yes the second star seems much fainter than 9.1 in the equivalent V band - and Eichorn's value is 9.65 for the second and 10.71 for the third. My values are even fainter relative to the primary - but they aren't calibrated and they use different filters.

Frank


Post Extras: Print Post   Remind Me!   Notify Moderator  
WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: STF450 - in search of evidence new [Re: freestar8n]
      #6327834 - 01/22/14 08:47 AM Attachment (7 downloads)

Frank, regarding the red color of the companion see the attached photo of Chris Thuemen (central part with STF450, horizontal and vertical flipped to match approximately the orientation of your photo).
Wilfried


Post Extras: Print Post   Remind Me!   Notify Moderator  
freestar8n
Post Laureate
*****

Reged: 10/12/07

Re: STF450 - in search of evidence [Re: WRAK]
      #6328669 - 01/22/14 03:26 PM

Thanks - yes it does look red. I was mainly trying to get linear measurements through filters so I could do quantitative magnitude comparisons of the companion stars with the primary. This isn't trivial because the star spots aren't exactly round and they overlap.

I will probably do it again but will calibrate the magnitudes with comparison stars.

But there are other more recent published values for the photometric magnitudes of the stars, and they are fainter than the 9.1 value.

Frank


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | (show all)


Extra information
1 registered and 1 anonymous users are browsing this forum.

Moderator:  PJ Anway, Rich (RLTYS), rflinn68 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 1983

Jump to

CN Forums Home




Cloudy Nights Sponsor: Astronomics