Quasar BTC40 J1429+011, Magnitude: 19.40, z=4.84 (missed it by that much!)

[Dennis]

I used the “Database Power Search Tool” in SkyTools 4 Imaging to select and download a list of Quasars in Virgo with a Redshift (z) between 4 and 6.

On that list I found BTC40 J1429+011 listed at Magnitude: 19.40 I, so I thought I’d fit my IR Pass IR742 filter and see if I could record this Quasar. An on-line search indicated the following:

SIMBAD Basic data :
[VV2006] J142926.5+011954 -- Quasar
ICRS coord. (ep=J2000): 14 29 26.4254653128 +01 19 53.572666764 (Optical)
B 24.55
V 22.53
G 20.579714
u (AB) 23.63
g (AB) 24.04
r (AB) 21.121
i (AB) 19.731
z (AB) 19.578

Although I could not hope to record objects at mag 23 or 24, I figured I might be in with a chance at i=19.731 using my IR742 Filter.

SkyTools 4 showed this Quasar with a Redshift (z): 4.84 and Light Time: 13.0 Gyr.

IMAGING DATA

• I captured 60x60 sec exposures.
  
• Tak Mewlon 210 F11.5
  
• Tak x0.8 Reducer
  
• ZWO ASI294MM Pro Camera
  
• Bin 2x2 (3126x2088 Pixels)
  
• IR Pass Filter IR742.
  
• Suburban Bortle 6/7 skies.
  

After Calibrating, Aligning and Stacking the frames, using averted vision and knowing the pre-conceived position of BTC40 J1429+011, I could just detect a faint smudge where the Quasar was meant to be, but I wouldn’t have bet the farm on it.

So, I had a fascinating journey into the universe of on-line Professional Resources and using SIMBAD and Aladin Lite, I managed to find a set of reference images which showed that my Quasar was indeed a “ghost”, an imaging artefact that had been amplified through image processing techniques such as mirco-contrast enhancement and deconvolution.

Oh well, for one brief moment I felt like I had nailed it, but it was not to be.

I have included the following images:

• Full FOV showing a 1600x1600 crop overlay
  
• My inverted 1600x1600 crop showing the “ghost” position of the Quasar.
  
• An enlarged composite showing the offset between the actual position and my "ghost" object.
  

Astrometry.Net Results for the 1600x1600 inverted crop.

• Center (RA, Dec): (217.333, 1.368)
  
• Center (RA, hms): 14h 29m 20.033s
  
• Center (Dec, dms): +01° 22' 03.673"
  
• Size: 11.7 x 11.7 arcmin
  
• Radius: 0.138 deg
  
• Pixel scale: 0.439 arcsec/pixel
  
• Orientation: Up is 359.9 degrees E of N
  

A composite image from Aladin Lite overlaid on my up-sample image showing the offset between the real Quasar and my candidate. Even though this offset is small, it is significant that all other objects faithfully line up with no offset.

Such is life.

Cheers

Dennis

   

   

   

[theskyhound]

That's cool. It seems to me that 60s is a really short sub exposure time. I know that systems vary, but still... did SkyTools recommend that? Or are you limited by tracking or something?

[PMSchu]

Dennis, it's odd that the quasar is a 'ghost'. Did you find additional 'ghost' objects on the image too? Is the Aladin image also an IR band image? At least we know that the quasar hasn't moved  .

Would you have been able to get better sensitivity without the IR filter or would the light pollution have overwhelmed the quasar's signal?

Still a nice effort.

Phil S.

[theskyhound]

Would you have been able to get better sensitivity without the IR filter or would the light pollution have overwhelmed the quasar's signal?

Just a reminder: the purpose of SkyTools is to answer a question like this.

[Dennis]

Dennis, it's odd that the quasar is a 'ghost'. Did you find additional 'ghost' objects on the image too? Is the Aladin image also an IR band image? At least we know that the quasar hasn't moved  .

Would you have been able to get better sensitivity without the IR filter or would the light pollution have overwhelmed the quasar's signal?

Still a nice effort.

Phil S.

Hi Pil

SkyTools showed a magnitude of "19.4 I" and I took the "I" to be Infrared, so fitted my IR742 Filter.

Some of the professional resources I browsed were imaging at between 800nm and 1200 nm which are longer wavelengths than my 742nm.

I'm not very familiar with the various aspects of Photometric Analysis, my only previous experience was in hunting down Star cluster Westerlund 1 using an IR807 IR Pass Filter which really made the stars pop, whereas in LRGB imaging the cluster was less conspicuous.

I sometimes use the IR642 for lunar imaging in poor seeing as the longer wavelengths of light are less affected.

Cheers

Dennis

---

That's cool. It seems to me that 60s is a really short sub exposure time. I know that systems vary, but still... did SkyTools recommend that? Or are you limited by tracking or something?

Hi Greg

I’m still in the process of commissioning the mount, which is taking so much longer than anticipated due to the effects of La Nina generating much more cloud cover than usual. Thankfully we are now exiting this cycle.

The mount is a SB Paramount MX+ and I am imaging at around 2100mm and provided I use the mount control SW to calibrate the mount, I can usually image for 30 secs and enjoy round stars at this FL.

60 secs is still good, but I begin to get some trailing, so these exposures are currently mount-limited at the moment (with no auto guiding) and the effects of having to set up and tear down each night.

The mount can be set up and configured with some one-time permanent SW settings and session-by-session calibration results that need to be refreshed each time I set up and tear down. If I had a permanent set up I could probably exceed 60 secs.

I will probably have to revert to auto guiding so I can dither the exposures as I am seeing a lot of fixed pattern noise which requires dithering to reduce its effects when stacking.

The whole commissioning process is taking longer as there is a Southern Hemisphere anomaly with the HW/SW system when trying to implement the mount’s PEC routine, and I have had to resort to 3rd party SW for an interim solution. More stuff to learn.

So, to cut a long story short, once I have mastered the nightly set up and tear down process, obtained a good PEC recording and fitted a guide scope, I’ll be able to make more use of the planning and exposure tools in ST4 and go much longer, notwithstanding my Bortle6/7 skies (I am on the borderline).

Cheers

Dennis

[theskyhound]

It may be worth trying again one day down the road when you can make longer sub exposures. I'm guessing, but I suspect longer subs will get you much deeper for the same total exposure time.

[Dennis]

It may be worth trying again one day down the road when you can make longer sub exposures. I'm guessing, but I suspect longer subs will get you much deeper for the same total exposure time.

Definitely, ST4 shows this as a good target up until mid-July for my location and we generally get clearer, more transparent skies in our winter down under. I will also plug in the IR807 and see what turns up.

There is something quite alluring about 13.0 Gyr.

Cheers

Dennis

[Dennis]

Dennis, it's odd that the quasar is a 'ghost'. Did you find additional 'ghost' objects on the image too? Is the Aladin image also an IR band image? At least we know that the quasar hasn't moved  .

Would you have been able to get better sensitivity without the IR filter or would the light pollution have overwhelmed the quasar's signal?

Still a nice effort.

Phil S.

Hi Phil

I managed to track down an on-line professional observatory image DECaLS DR3 Colour of the region and it shows the Quasar.

When I overlay my image, my “ghost” Quasar is clearly offset but it does appear to match a fainter object on the Pro Image. So, my “Ghost” may not be an imaging or processing artefact after all, but it is not the desired Quasar.

Cheers

Dennis

DECaLS DR3 Colour ref Image
   

Quasar Circled
   

Dennis' Image
   

Comparison Overlay
   

[PMSchu]

Dennis, that is SO close! Some of the bright stars aren't prefectly aligned either, but they're much larger, so the true position is harder to determine. It doesn't look like there's a similar artifact elsewhere on your image, but the mystery object is right at the detection limit of the exposures. Funny that the artifact appears where the quasar should be, or close anyway. I suppose that's how those things work.

Perhaps another 60x60 seconds of exposures will answer the question. When in doubt - collect more data.

Phil S.

[Bobbo]

I'm guessing, but I suspect longer subs will get you much deeper for the same total exposure time.

Is this something that ST can be used to determine?