by Ann » Tue Jan 09, 2024 7:29 pm
RandyM wrote: ↑Tue Jan 09, 2024 6:12 pm
Thanks for APOD! Why is one star, located above the helmet at the 1 o'clock position and within the wings, so red?
There is a star in this position,
HD 57057, which is quite red. Its B-V index is almost +2.0, which is quite red for stars.
HD 57057 is apparently a giant, very cool, very luminous star. It's very distant too, at some 11,000 light-years away from us. Its V luminosity of 8.77 magnitudes means it's emitting some 3,000 times the light of the Sun in yellow-green light. In infrared light, at a wavelength described as J (I'll let someone else check exactly what wavelength that is), the star is much brighter, some 120,000 times the luminosity of the Sun.
Simbad Astronomical Database described HD 57057 as a long-period variable.
Wikipedia wrote:
Long period variables are pulsating cool giant, or supergiant, variable stars with periods from around a hundred days, or just a few days for OSARGs, to more than a thousand days. In some cases, the variations are too poorly defined to identify a period, although it is an open question whether they are truly non-periodic.[8]
LPVs have spectral class F and redwards, but most are spectral class M, S or C. Many of the reddest stars in the sky, such as Y CVn, V Aql, and VX Sgr are LPVs.
Most LPVs, including all Mira variables, are thermally-pulsing asymptotic giant branch stars with luminosities several thousand times the sun. Some semiregular and irregular variables are less luminous giant stars, while others are more luminous supergiants including some of the largest known stars such as VY CMa.
If many long-period variables are asymtotic giant branch stars, then they are on their last legs before they shed their atmospheres and become planetary nebulas and white dwarfs. These stars are typically both very red and really quite bright.
So we can probably say that HD 57057 is about to die, just like the famous Mira, but it's putting on one final bright red light show before its spectacular death.
Ann
[quote=RandyM post_id=336218 time=1704823956]
Thanks for APOD! Why is one star, located above the helmet at the 1 o'clock position and within the wings, so red?
[/quote]
There is a star in this position, [url=https://simbad.u-strasbg.fr/simbad/sim-basic?Ident=SAO+152707&submit=SIMBAD+search]HD 57057[/url], which is quite red. Its B-V index is almost +2.0, which is quite red for stars.
[attachment=0]HD 57057 long period variable.png[/attachment]
HD 57057 is apparently a giant, very cool, very luminous star. It's very distant too, at some 11,000 light-years away from us. Its V luminosity of 8.77 magnitudes means it's emitting some 3,000 times the light of the Sun in yellow-green light. In infrared light, at a wavelength described as J (I'll let someone else check exactly what wavelength that is), the star is much brighter, some 120,000 times the luminosity of the Sun.
[url=https://simbad.u-strasbg.fr/simbad/sim-basic?Ident=SAO+152707&submit=SIMBAD+search]Simbad Astronomical Database[/url] described HD 57057 as a long-period variable.
[quote][url=https://en.wikipedia.org/wiki/Long-period_variable_star#Properties]Wikipedia[/url] wrote:
Long period variables are pulsating cool giant, or supergiant, variable stars with periods from around a hundred days, or just a few days for OSARGs, to more than a thousand days. In some cases, the variations are too poorly defined to identify a period, although it is an open question whether they are truly non-periodic.[8]
LPVs have spectral class F and redwards, but most are spectral class M, S or C. Many of the reddest stars in the sky, such as Y CVn, V Aql, and VX Sgr are LPVs.
Most LPVs, including all Mira variables, are thermally-pulsing asymptotic giant branch stars with luminosities several thousand times the sun. Some semiregular and irregular variables are less luminous giant stars, while others are more luminous supergiants including some of the largest known stars such as VY CMa.[/quote]
If many long-period variables are asymtotic giant branch stars, then they are on their last legs before they shed their atmospheres and become planetary nebulas and white dwarfs. These stars are typically both very red and really quite bright.
[img3="Globular cluster NGC 6397. Normally, the brightest, reddest stars of globular clusters are asymtotic giant branch stars, which are about to kick the bucket on their fusion lifeline and become planetary nebulas and white dwarfs. Credit: Credit:
NASA, ESA, and T. Brown and S. Casertano (STScI)
Acknowledgement: NASA, ESA, and J. Anderson (STScI)"]https://cdn.esahubble.org/archives/images/screen/opo1824a.jpg[/img3]
So we can probably say that HD 57057 is about to die, just like the famous Mira, but it's putting on one final bright red light show before its spectacular death.
[img3="Famous long-period soon-to-be-dead bright red star Mira. No one puts Mira in a corner, except perhaps DSS 2/ESO. Credit: DSS 2/ESO"]https://upload.wikimedia.org/wikipedia/commons/thumb/b/b0/A_Wide-field_view_of_the_sky_around_a_field_studied_in_the_MASSIV_survey.jpg/800px-A_Wide-field_view_of_the_sky_around_a_field_studied_in_the_MASSIV_survey.jpg[/img3]
Ann