M52 Cassiopeia Salt & Pepper Cluster

M52 Cassiopeia Salt & Pepper Cluster; Captured at HCH, Colorado Springs, Colorado with Big Zeus and L-eXtreme light pollution filter on 14 September 2024

Fun facts

M52 Cassiopeia Salt & Pepper Cluster: Messier 52 or M52, also known as NGC 7654 or the Scorpion Cluster, is an open cluster of stars in the highly northern constellation of Cassiopeia. It was discovered by Charles Messier in 1774.  It can be seen from Earth under a good night sky with binoculars.  The brightness of the cluster is influenced by extinction, which is stronger in the southern half.  Its metallicity is somewhat below that of the Sun, and is estimated to be [Fe/H] = −0.05 ± 0.01.

R. J. Trumpler classified the cluster appearance as II2r, indicating a rich cluster with little central concentration and a medium range in the brightness of the stars.  This was later revised to I2r, denoting a dense core.  The cluster has a core radius of 2.97 ± 0.46 ly (0.91 ± 0.14 pc) and a tidal radius of 42.7 ± 7.2 ly (13.1 ± 2.2 pc).   It has an estimated age of 158.5 million years and a mass of 1,200 M☉.

The magnitude 8.3 supergiant star BD +60°2532 is a probable member of the cluster, so too 18 candidate slowly pulsating B stars, one being a Delta (δ) Scuti variable, and three candidate Gamma Doradus (γ Dor) variables. There may also be three Be stars.  The core of the cluster shows a lack of interstellar matter, which may be due to supernovae explosion(s) early in the cluster’s history.

Other Catalog Designations: NGC 7654, Cr 455, C 2322+613, OCl 260
Subtype: Open star cluster
Distance from Earth: 4600 light years (1.4 kpc)
Apparent Size: 13.0′
Size: 9.5 light years (radius)
Mass: 1,200 M☉
Estimated age: 158.5 million years
Magnitude: 7.3
Constellation: Cassiopeia

{Target information derived from: https://en.wikipedia.org/wiki/Messier_52 }


Capture & Processing Notes

As background, from my 6 September 2024 imaging of IC5146 Cocoon Nebula… The autoguider decided not to work reliably throughout the night.  It would connect fine, conduct the calibration at the beginning of each sequence, pause during auto-focus (while I was watching it), and resume.  But it stopped unexpectedly during the sequence – first at about an hour into the sequence from the start that I discovered when I went out at midnight to conduct the meridian flip.  Second about two hours into the sequence after the meridian flip.  Both times the error message in PHD2 stated “ASCOM driver disconnected, check cabling or driver.”  All the cabling was fine and still attached.  Originally, I thought it was because the cable was too short and with all the cabling in a bundle, a straining may have pulled on the cabling to cause it to electrically disconnect, causing the autoguider to fail (need to check to make sure that laptop has auto-recovery set up correctly and selected).  Then after looking at the timing of the disconnect, I’m beginning to wonder if it had to do with the pause during auto-focus that it couldn’t recover from. 

With that as background for this image… The last “missing piece” of the EAF puzzle fell into place!  As I’d suspected, the autoguider was not coming back from its pause while the autofocus was running.  I came out an hour after I’d started the Tulip Nebula sequence to find SGP was in recovery mode, stating “Something terrible has happened and we’re trying to recover.”  It was indeed trying to recover from PHD2 having lost its guide stars.   At that point I turned off the autofocuser, noting the time, so I could contact SGP support in the morning with the log and point to the time the error occurred.  While I laid in bed “sleeping” it occurred to me that I could do an experiment to run the autofocuser while the autoguider was running to see if it would resolve a good focus point.  When I went out to switch targets, I opened the M52 Cassiopeia Salt & Pepper Cluster sequence and went into the control panel to make that change in the settings.  While I was hovering over the check box, I read the instructions (there I go again…) and it said that function was meant for off-axis guiders (OAG) because when the autofocuser takes the stars too much out of focus, it may lose track.  Hmm, I don’t have an OAG, so this may be worth a try!  I unchecked the “pause autoguiding during focus” and started the sequence.  Low and behold – it worked!  I came out at the one-hour point from the start of the beginning of the M52 sequence execution, and it was in the midst of the autofocus routine.  The autofocus routine completed successfully, the autoguider conducted its dither, and the sequence started up again on the next subframe collection!  So, yet again, it was my settings and not an issue with any of the hardware or software (or their integration) that was causing the problem. 

Although this was a “first” with BZ and LeX I didn’t run the SGP step-size experiment.  I used the 150-step size from the BB-LeX experiment on 27Aug2024, going with the theory that it’s the filter and not the telescope that matters (although there’s probably a mix of both, but both BB and BZ are f/8.0). I collected the data during each run of the autofocuser – to ensure that the step size was producing the correct change in star HFR value – which it was. 

Sequence Plan (14Sep2024): Gain: 158, Temp: -0°C, offset=30. 38x5min, Total = 190min (3:10hrs).  Captured 15Sep2024, 02:13MDT – 05:43MDT. 

Processing:  Captured in SGP, stacked in APP (Ha-OIII Color), processing with LR/PS


Equipment

All equipment controlled by HP Probook (DSO CTRL 2) Windows 10 laptop running Sequence Generator Pro vv4.4.1.1413..  

  • Imaging (ASI2400-BZ-LeX): ZWO ASI2400MC imaging camera on (Big Zeus) Orion 10″ f/8 Ritchey-Chretien Astrograph Telescope, Teleskop Service Flattener 1.0x for RC Telescopes (TS-RCFLAT2), Optolong L-eXtreme LP filter (LeX)
  • Autofocuser: ZWO EAF Electronic Automatic Focuser (EAF-5V-STD)
  • Mount: Rainbow Astro RST-300 (controlled by iHubo ASCOM driver)
  • Polar alignment: QHYCCD camera (controlled by Polemaster for polar alignment)
  • Autoguiding:  Orion 60mm Multi-Use Guide Scope with Orion StarShoot AutoGuider Pro Mono Astrophotography Camera (controlled by PHD2)onic Automatic Focuser)

Summary

Captured: 15 September 2024, from HCH Colorado Springs, Colorado (190min, or 3:10hrs imaging time)
Equipment: Big Zeus, LeX filter, ZWO EAF, Rainbow Astro RST-300
Processed: Captured in SGP, stacked in APP, star removal in Starnet++, processed in LR/PS