اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSALT HRS discovery of the binary nucleus of the Etched Hourglass Nebula MyCn 18
70
0
0.0
(
0
)
تأليف
Brent Miszalski
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The shaping of various morphological features of planetary nebulae (PNe) is increasingly linked to the role of binary central stars. Identifying a binary within a PN offers a powerful tool with which to directly investigate the formation mechanisms behind these features. The Etched Hourglass Nebula, MyCn 18, is the archetype for several binary-linked morphological features, yet it has no identified binary nucleus. It has the fastest jets seen in a PN of 630 km s$^{-1}$, a central star position offset from the nebula centre, and a bipolar nebula with a very narrow waist. Here we report on the Southern African Large Telescope (SALT) High Resolution Spectrograph (HRS) detection of radial velocity variability in the nucleus of MyCn 18 with an orbital period of $18.15pm0.04$ days and a semi-amplitude of $11.0pm0.3$ km s$^{-1}$. Adopting an orbital inclination of $38pm5$ deg and a primary mass of $0.6pm0.1$ $M_odot$ yields a secondary mass of $0.19pm0.05$ $M_odot$ corresponding to an M5V companion. The detached nature of the binary rules out a classical nova (CN) as the origin of the jets or the offset central star as hypothesised in the literature. Furthermore, scenarios that produce the offset central star during the AGB and that form narrow waist bipolar nebulae result in orbital separations 80--800 times larger than observed in MyCn 18. The inner hourglass and jets may have formed from part of the common envelope ejecta that remained bound to the binary system in a circumbinary disk, whereas the offset central star position may best be explained by proper motion. Detailed simulations of MyCn 18 are encouraged that are compatible with the binary nucleus to further investigate its complex formation history.
قيم البحث
اقرأ أيضاً
Whether planetary nebulae (PNe) are predominantly the product of binary stellar evolution as some population synthesis models (PSM) suggest remains an open question. Around 50 short period binary central stars ($Psim1$ d) are known, but with only fou
r with measured orbital periods over 10 d, our knowledge is severely incomplete. Here we report on the first discovery from a systematic SALT HRS survey for long period binary central stars. We find a 142 d orbital period from radial velocities of the central star of NGC~1360, HIP~16566. NGC~1360 appears to be the product of common-envelope (CE) evolution, with nebula features similar to post-CE PNe, albeit with an orbital period considerably longer than expected to be typical of post-CE PSM. The most striking feature is a newly-identified ring of candidate low-ionisation structures (LIS). Previous spatio-kinematic modelling of the nebula gives a nebula inclination of $30pm10$ deg, and assuming the binary nucleus is coplanar with the nebula, multi-wavelength observations best fit a more massive, evolved WD companion. A WD companion in a 142 d orbit is not the focus of many PSM, making NGC~1360 a valuable system with which to improve future PSM work. HIP~16566 is amongst many central stars in which large radial velocity variability was found by low-resolution surveys. The discovery of its binary nature may indicate long period binaries may be more common than PSM models predict.
EGB 6 is a faint, large, ancient planetary nebula (PN). Its central star, a hot DAOZ white dwarf (WD), is a prototype of a rare class of PN nuclei associated with dense, compact emission-line knots. The central star also shows excess fluxes in both t
he near- (NIR) and mid-infrared (MIR). In a 2013 paper, we used Hubble Space Telescope (HST) images to show that the compact nebula is a point-like source, located 0.16 (~118 AU) from the WD. We attributed the NIR excess to an M dwarf companion star, which appeared to coincide with the dense emission knot. We now present new ground-based NIR spectroscopy, showing that the companion is actually a much cooler source with a continuous spectrum, apparently a dust-enshrouded low-luminosity star. New HST images confirm common proper motion of the emission knot and red source with the WD. The I-band, NIR, and MIR fluxes are variable, possibly on timescales as short as days. We can fit the spectral-energy distribution with four blackbodies (the WD, a ~1850 K NIR component, and MIR dust at 385 and 175 K). Alternatively, we show that the NIR/MIR SED is very similar to that of Class 0/I young stellar objects. We suggest a scenario in which the EGB 6 nucleus is descended from a wide binary similar to the Mira system, in which a portion of the wind from an AGB star was captured into an accretion disk around a companion star; a remnant of this disk has survived to the present time, and is surrounded by gas photoionized by UV radiation from the WD.
EGB6 is an extended, faint old planetary nebula (PN) with an enigmatic nucleus. The central star (PG0950+139) is a hot DAOZ-type white dwarf (WD). An unresolved, compact emission knot was discovered to be located 0.166 away from the WD and it was sho
wn to be centered around a dust-enshrouded low-luminosity star. It was argued that the dust disk and evaporated gas (photoionized by the hot WD) around the companion are remnants of a disk formed by wind material captured from the WD progenitor when it was an asymptotic giant branch (AGB) star. In this paper, we assess the hot WD to determine its atmospheric and stellar parameters. We performed a model-atmosphere analysis of ultraviolet (UV) and optical spectra. We found Teff = 105,000 +/- 5000 K, log g = 7.4 +/- 0.4, and a solar helium abundance (He = 0.25 +/- 0.1, mass fraction). We measured the abundances of ten more species (C, N, O, F, Si, P, S, Ar, Fe, Ni) and found essentially solar abundance values, indicating that radiation-driven wind mass-loss, with a theoretical rate of log(dot-M/M_sun/yr) = -11.0 (+1.1)(-0.8) prevents the gravitational separation of elements in the photosphere. The WD has a mass of M/M_sun = 0.58 (+0.12)(-0.04) and its post-AGB age (log(t_evol/yr) = 3.60 (+1.26)(-0.09)) is compatible with the PN kinematical age of log(t_PN}/yr) = 4.2. In addition, we examined the UV spectrum of the hot nucleus of a similar object with a compact emission region, TOL26 (PN G298.0+34.8), and found that it is a slightly cooler DAOZ WD (Teff about 85,000 K), but this WD shows signatures of gravitational settling of heavy elements.
The Chandra X-ray Observatory has detected relatively hard X-ray emission from the central stars of several planetary nebulae (PNe). A subset have no known late-type companions, making it very difficult to isolate which of several competing mechanism
s may be producing the X-ray emission. The central star of NGC 2392 is one of the most vexing members, with substantial indirect evidence for a hot white dwarf (WD) companion. Here we report on the results of a radial velocity (RV) monitoring campaign of its central star with the HERMES echelle spectrograph of the Flemish 1.2 m Mercator telescope. We discover a single-lined spectroscopic binary with an orbital period of $1.902208pm0.000013$ d and a RV semi-amplitude of $9.96pm0.13$ km/s. The high degree of nebula ionisation requires a WD companion ($Mgtrsim0.6 M_odot$), which the mass-function supports at orbital inclinations $lesssim$7 deg, in agreement with the nebula orientation of 9 deg. The hard component of the X-ray spectrum may be explained by the companion accreting mass from the wind of the Roche lobe filling primary, while the softer component may be due to colliding winds. A companion with a stronger wind than the primary could produce the latter and would be consistent with models of the observed diffuse X-ray emission detected in the nebula. The diffuse X-rays may also be powered by the jets of up to 180 km/s and active accretion would imply that they could be the first active jets of a post-common-envelope PN, potentially making NGC 2392 an invaluable laboratory to study jet formation physics. The 1.9 d orbital period rules out a double-degenerate merger leading to a Type Ia supernova and the weak wind of the primary likely also precludes a single-degenerate scenario. We suggest that a hard X-ray spectrum, in the absence of a late-type companion, could be a powerful tool to identify accreting WD companions.
We present a detailed investigation of SBS1150+599A, a close binary star hosted by the planetary nebula PN G135.9+55.9 (TS01, Stasinska et al, 2009). The nebula, located in the Galactic halo, is the most oxygen-poor one known to date and is the only
one known to harbor a double degenerate core. We present XMM-Newton observations of this object, which allowed the detection of the previously invisible component of the binary core, whose existence was inferred so far only from radial velocity and photometric variations. The parameters of the binary system were deduced from a wealth of information via three independent routes using the spectral energy distribution (from the infrared to X-rays), the light and radial velocity curves, and a detailed model atmosphere fitting of the stellar absorption features of the optical/UV component. We find that the cool component must have a mass of 0.54+/-0.2 Msun, an average effective temperature, Teff, of 58000+/-3000 K, a mean radius of 0.43+/-0.3 Rsun, a gravity log g=5.0+/-0.3, and that it nearly fills its Roche lobe. Its surface elemental abundances are found to be: 12 + log He/H = 10.95+/-0.04 dex, 12 + log C/H = 7.20+/-0.3 dex, 12 + log N/H < 6.92 and 12 + log O/H < 6.80, in overall agreement with the chemical composition of the planetary nebula. The hot component has Teff = 160-180 kK, a luminosity of about ~10e4 Lsun and a radius slightly larger than that of a white dwarf. It is probably bloated and heated as a result of intense accretion and nuclear burning on its surface in the past. The total mass of the binary system is very close to Chandrasekhar limit. This makes TS01 one of the best type Ia supernova progenitor candidates. We propose two possible scenarios for the evolution of the system up to its present stage.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
