An In Situ Study of Turbulence near Stellar Bow Shocks
Abstract Stellar bow shocks are observed in a variety of interstellar environments and shaped by the conditions of gas in the interstellar medium (ISM). In situ measurements of turbulent density fluctuations near stellar bow shocks are only achievable with a few observational probes, including H α -emitting bow shocks and the Voyager Interstellar Mission (VIM). In this paper, we examine density variations around the Guitar Nebula, an H α bow shock associated with PSR B2224+65, in tandem with density variations probed by VIM near the boundary of the solar wind and ISM. High-resolution Hubble Space Telescope observations of the Guitar Nebula taken between 1994 and 2006 trace density variations over scales from hundreds to thousands of au, while VIM density measurements made with the Voyager 1 Plasma Wave System constrain variations from thousands of meters to tens of au. The power spectrum of density fluctuations constrains the amplitude of the turbulence wavenumber spectrum near the Guitar Nebula to log 10 C n 2 = − 0.8 ± 0.2 m −20/3 and for the very local ISM probed by Voyager to log 10 C n 2 = − 1.57 ± 0.02 m −20/3 . Spectral amplitudes obtained from multiepoch observations of more »
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Publication Date:
NSF-PAR ID:
10321808
Journal Name:
The Astrophysical Journal
Volume:
922
Issue:
2
ISSN:
0004-637X
Tight binary or multiple-star systems can interact through mass transfer and follow vastly different evolutionary pathways than single stars. The star TYC 2597-735-1 is a candidate for a recent stellar merger remnant resulting from a coalescence of a low-mass companion with a primary star a few thousand years ago. This violent event is evident in a conical outflow (“Blue Ring Nebula”) emitting in UV light and surrounded by leading shock filaments observed in Hαand UV emission. From Chandra data, we report the detection of X-ray emission from the location of TYC 2597-735-1 with a luminosity$log(LX/Lbol)=−5.5$. Together with a previously reported period of ~14 days, this indicates ongoing stellar activity and the presence of strong magnetic fields on TYC 2597-735-1. Supported by stellar evolution models of merger remnants, we interpret the inferred stellar magnetic field as dynamo action associated with a newly formed convection zone in the atmosphere of TYC 2597-735-1, though internal shocks at the base of an accretion-powered jet cannot be ruled out. We speculate that this object will evolve into an FK Com–type source, i.e., a class of rapidly spinning magnetically active stars for which a merger origin has beenmore »
4. Voyager 1 (V1) has been exploring the heliospheric boundary layer in the very local interstellar medium (VLISM) since August 2012. This study presents a broadband multi-scale analysis of VLSIM magnetic turbulence between 124 and 144 au from the Sun, as observed by V1 during the period from 2013.36 to 2019.0. We use high resolution 48-s data and show the existence of physically relevant fluctuations on scales as small as the ion inertial length in the thermal plasma. In the fine-scale regime below $\sim 10^{-3}$ au, an evidence is provided of the intermittent turbulence cascade which retains a significant level of magnetic compressibility. Observed fluctuations are compatible with the presence of filamentary structures and sawtooth-like waveforms of mixed compressible/transverse nature. A striking example of small-scale enhanced turbulence (wavelengths in the range of $\sim 1-10^3$ ion inertial lengths) is observed in front of the shock wave that overtook V1 on DOY 237, 2014 at 140 au from the Sun. This event starts on DOY 178, 2014, and suggests the presence of an ion foreshock. Besides, small-scale intermittency has been growing smoothly since 2018.5. Our analysis suggests that local processes are contributing to the production of turbulence in this regime. We identified themore »