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Contains:  NGC 6723, NGC 6726, The star εCrA
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The Heart of Corona Australis, 



    
        

            Gabriel R. Santos...
The Heart of Corona Australis
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The Heart of Corona Australis

Technical card


Dates:July 8, 2019

Frames: 130x180" ISO1600

Integration: 6.5 hours

Darks: ~25

Flats: ~20

Bias: ~50

Avg. Moon age: 6.37 days

Avg. Moon phase: 39.27%

Bortle Dark-Sky Scale: 3.00

Mean SQM: 21.70

Mean FWHM: 3.10

Temperature: -2.00


Basic astrometry details

Astrometry.net job: 3112428

RA center: 19h 1' 27"

DEC center: -37° 2' 31"

Pixel scale: 1.885 arcsec/pixel

Orientation: 355.371 degrees

Field radius: 1.084 degrees


Resolution: 3446x2297

Locations: Sítio, Cristina, MG, Brazil

Data source: Traveller

Description

This great starfield shows the central part of Corona Australis and part of its molecular cloud of dust. Between the dust, stars shine in the main star-forming region near NGC 6726-27, some 500 light years away. It features some very interesting objects: reflection nebulae, with the characteristic blue color; the variable R CrA and its associated yellowish variable nebula NGC 6729; several Herbig-Haro objects subject to scientific research, and a lot of very faint dust [1]. “Buried in the dust is a star formation that has given the dark cloud a faint yellow glow and produced a number of small, red nebulae” [2]. The globular cluster NGC 6523, although appearing to be in the same plane as the nebulae, is only juxtaposed from our point of view, lying much further at 28000 light years away [3].

Herbig-Haro objects are bright patches of nebulosity associated with newborn stars, usually found in star-forming regions, formed with the collision of narrow jets of partially ionised gas ejected by stars with nearby clouds of gas and dust at several hundred kilometres per second. In this image they’re tiny bright yellowish-redish nebulae. Interestingly they can evolve visibly in a timescale of a few years. It is quite unusual for us to see astronomical “change”, as our lives are so short in the astronomical timescales, but HH objects present a wonderful challenge: Terry Robison’s image is mesmerizing, showing a 4 year comparison of one of these objects in CrA.
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This image was acquired with my Newtonian 150mm astrograph during my July 2019 holidays. Those were probably the most beautiful nights I have experienced there yet. A few days after rain, the atmosphere was crystal clear, great transparency and seeing. The very faint airglow was easily captured in wide angle exposures, and, along the DSO images, I acquired some great panoramas and nightscapes as well. Besides, those were the most challenging conditions as well – temperatures plummeted with the dry and cold air mass, and from 11 pm onwards it was already below freezing. The lowest temperature, at 6:30 am, was -4ºC! Frost (“geada” in Portuguese) covered the early morning landscape: a beautiful sight (the OTA was also completely covered in frost!).

This particular image started about 11pm, with the rig shooting until sunrise while I slept =D. The data was remarkable, as the night conditions were perfect. Not a single lost sub. However, upon closer examination I noticed some faint large halos in the brightest stars. My only conclusion was the extreme cold and relative humidity caused one of my mirrors (or corrector lenses) to form a little bit of dew, especially on the edges, despite having the dew heater on the secondary turned on (I believe the primary was the one which dewed). Unfortunately, all the 6.5h had those halos, which impacted the nebulosity detail near the brightest stars, but provided a somewhat artistic look. This had a sensibly negative effective, but I was still really happy with the final results! I was pleased to see extremely sharp data (focus was spot on), and the longer integration revealed quite a bit of nebulosity with sufficient SNR – this is my longest single frame integration! If you want, I further recommend checking the inspirational works by Fabian Neyer, Wei-Hao Wang, Hisayoshi Kato, Terry Robison and Tommy Nawratil on the area.

Constructive criticism, comments and suggestions are more than welcome in the comments section. Thank you for taking your time to look at this image!

Date: 7 and 8 July 2019
Location: MG, Brazil. Rural Skies (Bortle 3-4, calculated SQM ~21.5)
Camera: Canon EOS T5/1200D (modded), at ISO 1600
Optics: 150/750mm ATM Newtonian Telescope (optics by Sandro Coletti) + TS-Optics MaxField 2" Coma Corrector
Mount: Sky-Watcher HEQ5, tracking, guided
Exposure Detail: 130x180s. Total integration 390min or 6.5h.

[1] APOD 2018/11/29
[2] D.Malin, A View of the Universe, 1st ed. Cambridge University Press, 1993, pp. 112.
[3] NGC 6723, in-the-sky.org. From “Catalog of Parameters for Milky Way Globular Clusters” (Harris 1996).

Comments

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grsotnas
Gabriel R. Santos...
License: None (All rights reserved)
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            Gabriel R. Santos...
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            Gabriel R. Santos...
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The Heart of Corona Australis, 



    
        

            Gabriel R. Santos...