Robert Fealey published on October 21st on forum post including beautiful picture above:
https://rochesterskies.org/forum/topic/observing-tonight/page/167/#post-13989
The December Sky and Telescope mag motivated me to get out early this morning and see if I could observe and photograph “The First White Dwarf” star in 40 Eridani; the latter is a triple star with the B component a white dwarf.
In the attached photo I used the 10 in SCT and Orion 6.3 M pixel camera with a 8 second exposure. The bright component A is quite overexposed (but did have a nice yellow color) and component C was quite faint (11.2 mag). Visually I could barely see the white dwarf B (9.5 mag) and seeing conditions were poor unfortunately.
Story of 40 Eridani
West of Orion’s Rigel in the northern reaches of the meandering constellation Eridanus shines a triple star system 40 Eridanus. It lies 16.3 light years from Earth, about twice as far as Sirius. The brightest member of this stellar trio is orange dwarf, a K-type main sequence star, that like Sun converts hydrogen into helium in its core.
In 1783, on January 31st William Hershel saw that this naked eye star has two faint companions. The tight dim pair was 1 1/3 arcminutes east of the orange dwarf, 40 Eridani A.
Two decades later Giuseppe Piazzi observed large proper motion of the 40 Eridani and published it in 1804, a sign it could be a close star. In the 1880s astronomers finally measured parallax and found distance value close to the current value 16.3 light years.
In early 20th century was known that 40 Eri B is type-A star with hot surface, but dim. It was lonely in lower left corner of the diagram spectral-type and luminosity, now known as a Hertzsprung-Russel diagram. It meant that it has to be small like Earth. The term white dwarf coined in 1922 Willem Luyten, student of Hertzsprung.
More details in the Sky & Telescope article The First White Dwarf Discovery.
Observe Write Dwarf!
Triple star 40 Eridani can be easily observed next to the famous constellation Orion. It’s visible by naked eye and it has name Keid, officially approved by IAU since 2016. Name Keid,in indigenous Arabic al-qaid, means “the Egg Shells” in unspecified ostrich’s nest. Below is one row from IAU table.
| IAU Name | Designation | ID | Const. | # | WDS_J | Vmag | RA(J2000) | Dec(J2000) | Approval Date |
| Keid | HR 1325 | ο2 | Eri | A | 04153-0739 | 4.43 | 63.817999° | -7.652872° | 2016-09-12 |
| Epoch | RA | Dec |
| J2000 | 04h 15m 16.31963s | −07° 39′ 10.3404″ |
| 2023 | 04h 16m 20.4s | −07° 37′ 05.7″ |
| 2025 | 04h 16m 26.6s | −07° 36′ 51.5″ |
If Keid is in your eyepiece, you should look for 9.5mag white dwarf, about two Jupiter diameters apart.
More information can be found e.g. at SIMBAD: 40 Eri A, 40 Eri B. Latest measurement from GAIA astrometry observatory gives parallax for Keid 199.6080124181338 mili-arc-seconds then distance is 16.34 ly.
40 Eridani – Keid at stellarium-web.org. Adjust time of observing in the right bottom corner as needed.
Another picture 40 Eridani by Robert Fealey, better seeing, on forum.
Links:
https://en.wikipedia.org/wiki/40_Eridani
https://en.wikipedia.org/wiki/Eridanus_(constellation)
https://en.wikipedia.org/wiki/White_dwarf
Sky & Telescope: INSIDE THE DECEMBER 2022 ISSUE
The First White Dwarf The road to discovering a new type of star was long and winding. By Ken Croswell
IAU Naming Stars
A Dictionary of Modern Star Names: A Short Guide to 254 Star Names and Their Derivations