by Ann » Mon Sep 23, 2019 6:46 am
MarkBour wrote: ↑Sat Sep 21, 2019 10:17 pm
Capture.PNG
Thank you Ann and Boomer!
Boomer, I had a momentary difficulty comparing your linked image of the Tulip (which then had an accompanying diagram locating Cygnus X-1) to today's APOD. But after staring at them for a bit, I think I can align the two images, with just a slight rotation. If I'm correct, then, incorporating the guidance in your linked image, I've circled the star that may be a companion to X-1 in both images, to the right.
I certainly may be incorrect. There was some mention that the companion was a blue star, but the one I've cricled seems to be the one that Ivan Eder was so labeling on his site.
Interestingly, your linked image was credited to Ivan Eder, but I doubt he is any relation to Robert Eder, who captured today's APOD. Also, oddly, the APOD link from Robert Eder's name below the image appears to be incorrect, at least when I click on it. Robert Eder posts on astrobin (and instagram) and can be found here:
https://www.astrobin.com/users/Robsi/
Like Art said, HD 226868 is an intrinsically blue star of spectral class B0Ib, which is to say that its surface temperature would be around 30,000 K, and its unreddened B-V index would be at least -0.20. It could well be even more negative (and thus bluer). But the apparent B-V index of HD 226868, as measured from the Earth, is +0.73. That is a huge amount of reddening.
The star "above HD 226868, V1674 Cyg, which looks slightly bluish, has a B-V index of +0.56. In other words, it looks bluer to us than HD 226868 does. But if V1674 Cyg is moderately unreddened, it could be as cool as spectral class F, around, perhaps, 7,000 K.
Ann
[quote=MarkBour post_id=295460 time=1569104265 user_id=141361]
[float=right]Capture.PNG[/float]
Thank you Ann and Boomer!
Boomer, I had a momentary difficulty comparing your linked image of the Tulip (which then had an accompanying diagram locating Cygnus X-1) to today's APOD. But after staring at them for a bit, I think I can align the two images, with just a slight rotation. If I'm correct, then, incorporating the guidance in your linked image, I've circled the star that may be a companion to X-1 in both images, to the right.
I certainly may be incorrect. There was some mention that the companion was a blue star, but the one I've cricled seems to be the one that Ivan Eder was so labeling on his site.
Interestingly, your linked image was credited to Ivan Eder, but I doubt he is any relation to Robert Eder, who captured today's APOD. Also, oddly, the APOD link from Robert Eder's name below the image appears to be incorrect, at least when I click on it. Robert Eder posts on astrobin (and instagram) and can be found here:
[url]https://www.astrobin.com/users/Robsi/[/url]
[/quote]
Like Art said, HD 226868 is an intrinsically blue star of spectral class B0Ib, which is to say that its surface temperature would be around 30,000 K, and its unreddened B-V index would be at least -0.20. It could well be even more negative (and thus bluer). But the apparent B-V index of HD 226868, as measured from the Earth, is +0.73. That is a huge amount of reddening.
The star "above HD 226868, V1674 Cyg, which looks slightly bluish, has a B-V index of +0.56. In other words, it looks bluer to us than HD 226868 does. But if V1674 Cyg is moderately unreddened, it could be as cool as spectral class F, around, perhaps, 7,000 K.
Ann