# Stars/X-rays

X-ray stars have surface temperatures starting at 300,000 K corresponding to a peak wavelength of 10 nm for the beginning of super soft X-ray sources.

## Degenerate stars

On the right is the deepest X-ray image ever obtained, made with over 7 million seconds of observing time with NASA's Chandra X-ray Observatory.
"Huge numbers of supermassive black holes are visible in a stunning new photo that astronomers said is the deepest X-ray image of the sky ever captured."
"The concentration of these light-gobbling monsters in the central region of the photo is unprecedented — the equivalent of 5,000 supermassive black holes over an area the size of the full moon, or 1 billion if extended across the entire night sky."
"With this one amazing picture, we can explore the earliest days of black holes in the universe and see how they change over billions of years."
"The image incorporates about 80 days' worth of data collected by NASA's Chandra X-ray Observatory spacecraft and covers a patch of sky 8.5 light-years across. About seven out of every 10 objects in the photo are supermassive black holes, which lie at the hearts of galaxies and contain 100,000 to 10 billion times the mass of the sun."
"It can be very difficult to detect black holes in the early universe, because they are so far away and they only produce radiation if they're actively pulling in matter. But by staring long enough with Chandra, we can find and study large numbers of growing black holes, some of which appear not long after the Big Bang."
"Analyses of this treasure trove suggest that supermassive black holes grew in bursts, rather than gradually, in the first 1 billion to 2 billion years after the Big Bang. In addition, the "seeds" of these behemoths are likely quite heavy, with masses between 10,000 and 100,000 times that of the sun."
"By detecting X-rays from such distant galaxies, we're learning more about the formation and evolution of stellar-mass and supermassive black holes in the early universe. We're looking back to times when black holes were in crucial phases of growth, similar to hungry infants and adolescents."

## Cygnus X-1

The balloon bourne telescope was launched for the High Energy Replicated Optics project on May 23, 2001, reaching an altitude of 39 km.
During an Aerobee rocket flight of 16 June 1964, Cygnus X-1 (Cyg X-1, or Cyg XR-1 in 1964) is one of the seven X-1 sources discovered.

## V3893 Sagittarii

Although V3893 Sagittarii (WR102) is spectral type WO$_2$, with a photospheric surface temperature of 210,000 K, it has not been detected as an X-ray source.

## WR 142

"For the most part, single WR stars are thought to follow the evolutionary path: O → (LBV/RSG) → WN → WC → WO → SN (or GRB) (Conti et al. 1983; Crowther 2007). The initial mass of the O star determines whether it passes through an intermediate luminous blue variable (LBV) or red supergiant (RSG) phase (Crowther 2007)."
"Crowther et al. (1998) developed a new classification scheme using primary and secondary oxygen line ratios that confirmed previous classifications of WR 142 as a member of the subclass WO2 (Barlow & Hummer 1982; Kingsburgh et al. 1995)."
"WR 142 just recently became the first WO star to be detected in the X-rays using XMM-Newton (Oskinova et al. 2009)."
"WR 142 resides in the open cluster Berkeley 87."
"Berkeley 87 [contains] B-supergiants including HD 229059, an O8.5–O9 star BD+36 4032, a possible LBV Be star V439 Cyg, and the pulsating M3-supergiant BC Cyg."
"WR 142 is detected by Chandra as an X-ray source at J202144.35+372230.7 [...] The X-ray position of WR 142 is in exact agreement with the Two Micron All Sky Survey (2MASS) position of J202144.35+372230.7. Additionally, the Chandra position has offsets from optical counterparts of only 0.20" from the USNO-B1.0 source at J202144.35+372230.9 and 0.23" from the Hubble Space Telescope (HST) GSC 2.3.2 source at J202144.36+372230.5. All offsets are well within the positional accuracy of Chandra."
"The X-rays from WR 142 are weak but extremely hard, with a mean photon energy of 4.31 keV [...] WR 142 does not exhibit any significant emission below 2 keV and there is no evidence of a soft component [...] We find only one event below 2 keV, with an energy of 1.89 keV. This is in contrast to a faint soft component at E ≤ 1 keV in the XMM-Newton EPIC MOS spectrum of WR 142 reported by Oskinova et al. (2009). Assuming that no variability occurred in the WR 142 source spectrum or N$_H$ between the two observations, the most likely explanation for this difference would be the much lower effective area of Chandra ACIS-I at low energies E ≤ 1 keV."
"The WR 142 spectrum is dominated by hard emission above 2 keV, while soft emission below 2 keV dominates the OB stars [the O8.5 III star BD+36 4032 and the B1 Ia star HD 229059]."
The "X-ray properties of WR 142 can be summarized as follows: (1) source structure is consistent with a point source at Chandra's angular resolution; (2) no significant variability is detected over a timescale of ≈1 day; (3) strong X-ray absorption below 2 keV, with an absorption column density (N$_H$) that is a factor of ≈3–4 greater than expected from published optical estimates; (4) no evidence for a soft X-ray component below 2 keV; (5) a spectrum dominated by hard X-rays above 2 keV that can be fit equally well using a very high temperature thermal plasma model or a power-law model; and (6) a relatively low X-ray luminosity log L$_X$(0.3–8 keV) = 30.7–30.8 erg s$^{−1}$ (at d = 1.23 kpc), which is ≈10 times less than found for two X-ray bright OB stars in Berkeley 87".
WR 142 has a photospheric surface temperature of 200,000 K.

## Abell 30

According to SIMBAD, the spectral type of the central star is WC5. These stars have a surface, or photospheric, temperature apparently between 79,000 and 89,000 K.