by Ann » Fri Jan 09, 2015 5:14 am
geckzilla wrote:Well, it may be deserved, but from this outsider's viewpoint it is also worth noting that you appear to have an ax to grind with the Hipparcos catalog which makes you prone to wanting it to be wrong.
You may be interested in a couple of paragraphs from
this paper specifically devoted to these two stars. There are uncertainties about them because no one has given them a really good look more recently other than that 2007 Hipparcos reduction (at least as far as I can find).
A.11. CrA-11 (HD 176269, HR 7169)
CrA-11, more commonly known as HD 176269, is an optically detected PMS star with a spectral type of B8V that was first observed by Knacke et al. (1973) as HR 7169 to be a possible member of the young stellar association near R CrA (~12' to the SW). Another B8V star ~12'' away, HR 7170 (HD 176270), was also listed as a possible member and we include it in Table 7. These two sources were detected, but not spatially resolved, by the IRAS (IRAS 18; Wilking et al. 1992) and EINSTEIN satellites (CrAPMS 10; Walter et al. 1997).
HD 176269 was observed in the near-infrared by Glass & Penston (1975) and is referred to in their Table 1 as source l; HD 176270 was also observed, and is listed as source k. Later, Patten (1998) does not classify the HD 176269/HD 176270 pair (which he calls source R05) as a likely association member: he finds a spectral type of B9V for the source and detects a ROSAT X-ray counterpart, however the source does not fulfill enough criteria for him to consider it an association member. Note that these stars are far enough afield so that they were not included as part of the Forbrich & Preibisch (2007) Chandra study.
HD 176269 was also detected with ISOCAM by O99, and is referred to as ISO-CrA 110 in their survey. ISO-CrA 110 was found to have a mid-infrared excess based on those observations so it is considered one of their YSO candidates. HD 176270 is referred to as ISO-CrA 111 in the same study, and it was not found to have a mid-infrared excess.
These studies are consistent with the Spitzer observations; we classify HD 176269 as a Class III based on the shape of its SED. Although we do not classify HD 176270 as a YSO candidate, it very likely is also a Class III based on its colors and SED shape (see Table 7). The SEDs of the two stars look similar out to 8 μm. However, at 24 μm, HD 176269 is much brighter than HD 176270. Neither source is detected at 70 μm.
Thanks for that info, Geck. As to what I can conclude from that science-speak, there is nothing there to really contradict the possibility that these two stars are gravitationally bound.
But let me get back to Hipparcos. I don't think it can always be trusted, but that doesn't mean that I think it is usually wrong. I don't.
But let's look at the Hipparcos parallaxes for the Trapezium cluster in the Orion Nebula. These are the Hipparcos parallaxes for the four brightest stars as referred to by Simbad database:
Theta 1 A Orionis: -52.82 [33.69] mas
Theta 1 B Orionis: (Simbad gives no parallax)
Theta 1 C Orionis: -13.00 [5.05] mas
Theta 1 D Orionis: -27.24 [8.21] mas
Note that all the three parallaxes given are certifiably wrong, because they are all negative. Negative parallaxes are impossible. An infinitely distant object would have a parallax of zero in a flat universe.
Not only are the three parallaxes all negative, but they also differ a lot among themselves.
I certainly realize that the Trapezium must be an almost impossibly difficult place to measure parallaxes. The area is tiny and crowded, the stars are orbiting very, very fast around their common center of gravity, and chaotically swirling clouds of dust and glowing ionized gas must make it absolute incredibly hard to measure the parallaxes of the stars correctly. But for all of that, the Trapezium is a good example of the "iffiness" I see in the Hipparcos data sometimes.
Ann
[quote="geckzilla"]Well, it may be deserved, but from this outsider's viewpoint it is also worth noting that you appear to have an ax to grind with the Hipparcos catalog which makes you prone to wanting it to be wrong.
You may be interested in a couple of paragraphs from [url=http://www.aanda.org/articles/aa/full_html/2012/08/aa19084-12/aa19084-12.html]this paper[/url] specifically devoted to these two stars. There are uncertainties about them because no one has given them a really good look more recently other than that 2007 Hipparcos reduction (at least as far as I can find).
[quote]A.11. CrA-11 (HD 176269, HR 7169)
CrA-11, more commonly known as HD 176269, is an optically detected PMS star with a spectral type of B8V that was first observed by Knacke et al. (1973) as HR 7169 to be a possible member of the young stellar association near R CrA (~12' to the SW). Another B8V star ~12'' away, HR 7170 (HD 176270), was also listed as a possible member and we include it in Table 7. These two sources were detected, but not spatially resolved, by the IRAS (IRAS 18; Wilking et al. 1992) and EINSTEIN satellites (CrAPMS 10; Walter et al. 1997).
HD 176269 was observed in the near-infrared by Glass & Penston (1975) and is referred to in their Table 1 as source l; HD 176270 was also observed, and is listed as source k. Later, Patten (1998) does not classify the HD 176269/HD 176270 pair (which he calls source R05) as a likely association member: he finds a spectral type of B9V for the source and detects a ROSAT X-ray counterpart, however the source does not fulfill enough criteria for him to consider it an association member. Note that these stars are far enough afield so that they were not included as part of the Forbrich & Preibisch (2007) Chandra study.
HD 176269 was also detected with ISOCAM by O99, and is referred to as ISO-CrA 110 in their survey. ISO-CrA 110 was found to have a mid-infrared excess based on those observations so it is considered one of their YSO candidates. HD 176270 is referred to as ISO-CrA 111 in the same study, and it was not found to have a mid-infrared excess.
These studies are consistent with the Spitzer observations; we classify HD 176269 as a Class III based on the shape of its SED. Although we do not classify HD 176270 as a YSO candidate, it very likely is also a Class III based on its colors and SED shape (see Table 7). The SEDs of the two stars look similar out to 8 μm. However, at 24 μm, HD 176269 is much brighter than HD 176270. Neither source is detected at 70 μm.[/quote][/quote]
Thanks for that info, Geck. As to what I can conclude from that science-speak, there is nothing there to really contradict the possibility that these two stars are gravitationally bound.
But let me get back to Hipparcos. I don't think it can always be trusted, but that doesn't mean that I think it is usually wrong. I don't.
But let's look at the Hipparcos parallaxes for the Trapezium cluster in the Orion Nebula. These are the Hipparcos parallaxes for the four brightest stars as referred to by Simbad database:
Theta 1 A Orionis: -52.82 [33.69] mas
Theta 1 B Orionis: (Simbad gives no parallax)
Theta 1 C Orionis: -13.00 [5.05] mas
Theta 1 D Orionis: -27.24 [8.21] mas
Note that all the three parallaxes given are certifiably wrong, because they are all negative. Negative parallaxes are impossible. An infinitely distant object would have a parallax of zero in a flat universe.
Not only are the three parallaxes all negative, but they also differ a lot among themselves.
I certainly realize that the Trapezium must be an almost impossibly difficult place to measure parallaxes. The area is tiny and crowded, the stars are orbiting very, very fast around their common center of gravity, and chaotically swirling clouds of dust and glowing ionized gas must make it absolute incredibly hard to measure the parallaxes of the stars correctly. But for all of that, the Trapezium is a good example of the "iffiness" I see in the Hipparcos data sometimes.
Ann