Nature of blackbody stars

Abstract

A selection of 17 stars in the Sloan Digital Sky Survey, previously identified as DC-class white dwarfs (WDs), has been reported to show spectra very close to blackbody radiation in the wavelength range from ultraviolet to infrared. Because of the absence of lines and other details in their spectra, the surface gravity of these objects has previously been poorly constrained, and their effective temperatures have been determined by fits to the continuum spectrum using pure helium atmosphere models. We computed model atmospheres with pure helium and H/He mixtures and used Gaia DR2 parallaxes that are available for 16 of the 17 selected stars to analyze their physical properties. We find that the atmospheres of the selected stars are very probably contaminated with a trace amount of hydrogen of −6 ≤ log(NH/NHe) ≤ −5.4. For the 16 stars with Gaia parallaxes, we calculate a mean stellar mass 0.606 ± 0.076 M⊙, which represents typical mass values and surface gravities (7.8 < logg < 8.3) for WDs.

Discovery of Blackbody Stars and the Accuracy of SDSS photometry

“…Their brightness together with these parallaxes suggests that these stars are white dwarfs with helium atmosphere with temperature too low to develop absorption line features. One may take them as DC white dwarfs by applying the observational criterion, but their physical nature are consistent with DB white dwarfs, as we confirmed in a later study (Serenelli et al 2018). An accrate examination are carried out using more precise broad-band photometric data.…”

“…We found that the helium atmosphere model can yield precisely these blackbody spectra when the temperature is 8000K to 11000K, and in particular when helium is contaminated with a trace amount (≈ 10 −8 − 10 −6 ) of hydrogen (Serenelli et al 2018): see Figure 4. This hydrogen abundance is too small to detect its absorption features in current spectroscopic observations.…”

Evidence of spectral evolution on the white dwarf sample from the Gaia mission

“…They concluded that this decrease in the DA mass distribution is an indicator that a fraction of DAs with masses around 0.7 M undergo spectral evolution, turning into DCs. It is important to notice that Ourique et al (2019) used pure-helium model to estimate parameters for non-DAs, which should lead to an overestimation in their masses (Bergeron et al 2019;Serenelli et al 2019), if their envelopes are contaminated by hydrogen. Bergeron et al (2019) proposed that pure helium atmosphere white dwarf models do not describe non-DA white dwarfs for effective temperatures below 11 000 K. They show that pure helium models results in higher masses than expected for non-DAs below 11 000 K, and hydrogen-helium mixed model mass determinations agree better with the mean mass for non-DAs, similar to the conclusion by Serenelli et al (2019).…”

Interstellar Communication Network. I. Overview and Assumptions

“…However, the optimal spectrum is only a one-dimensional blackbody 3 for the special case where all of the power transmitted is intercepted by the receiver, but only one spatial mode is used (Fresnel number D(f ) = 1). Such an emitter can be distinguished from natural sources because most known astrophysical bodies are not perfect blackbodies, with exceptions being the Schwarzschild radiation of a black hole (Hawking 1975) , the cosmic microwave background (Hsu & Zee 2006), and DB white dwarfs (Suzuki & Fukugita 2017;Serenelli et al 2019)). An artificial construct which processes information at maximum efficiency would be very close to the CMB temperature and could be incidentally hard to detect ( Ćirković & Bradbury 2006).…”