We report on nine wide common proper motion systems containing late-type M, L, or T companions. We confirm six previously reported companions, and identify three new systems. The ages of these ...systems are determined using diagnostics for both stellar primaries and low-mass secondaries and masses for the secondaries are inferred using evolutionary models. Of our three new discoveries, the M3+T6.5 pair G 204-39 and SDSS J1758+4633 has an age constrained to 0.5-1.5 Gyr making the secondary a potentially useful brown dwarf benchmark. The G5+L4 pair G 200-28 and SDSS J1416+5006 has a projected separation of ~25,000 AU making it one of the widest and lowest binding energy systems known to date. The system containing NLTT 2274 and SDSS J0041+1341 is an older M4+L0 (>4.5 Gyr) pair which shows H Delta *a activity in the secondary but not the primary making it a useful tracer of age/mass/activity trends. Two of the nine systems have discrepant component ages that emerge from stellar or ultracool diagnostics indicating possible shortcomings in our understanding of the age diagnostics of stars and brown dwarfs. We find a resolved binary frequency for widely separated (>100 AU) low-mass companions (i.e., at least a triple system) which is at least twice the frequency found for the field ultracool dwarf population. The ratio of triples to binaries and quadruples to binaries is also high for this sample: 3:5 and 1:4, respectively, compared to 8 pc sample values of 1:4 and 1:26. The additional components in these wide companion systems indicates a formation mechanism that requires a third or fourth component to maintain gravitational stability or facilitate the exchange of angular momentum. The binding energies for the nine multiples discussed in this text are among the lowest known for wide low-mass systems, suggesting that weakly bound, low-to-intermediate mass (0.2 M < M tot< 1.0 M ) multiples can form and survive to exist in the field (1-8 Gyr).
N103B is a Type Ia supernova remnant (SNR) projected in the outskirts of the superbubble around the rich cluster NGC 1850 in the Large Magellanic Cloud (LMC). We have obtained H and continuum images ...of N103B with the Hubble Space Telescope (HST) and high-dispersion spectra with the 4 m and 1.5 m telescopes at Cerro Tololo Inter-American Observatory. The HST H image exhibits a complex system of nebular knots inside an incomplete filamentary elliptical shell that opens to the east, where X-ray and radio emission extends farther out. Electron densities of the nebular knots, determined from the S ii doublet, reach 5300 cm−3, indicating an origin of circumstellar medium, rather than interstellar medium. The high-dispersion spectra reveal three kinematic components in N103B: (1) a narrow component with N ii λ6583/H ∼ 0.14 from the ionized interstellar gas associated with the superbubble of NGC 1850 in the background, (2) a broader H component with no N ii counterpart from the SNR's collisionless shocks into a mostly neutral ambient medium, and (3) a broad component, ∼ 500 km s−1, in both H and N ii lines from shocked material in the nebular knots. The Balmer-dominated filaments can be fitted by an ellipse, and we adopt its center as the site of SN explosion. We find that the star closest to this explosion center has colors and luminosity consistent with a 1 surviving subgiant companion as modeled by Podsiadlowski. Follow-up spectroscopic observations are needed to confirm this star as the SN's surviving companion.
It has recently been discovered that some, if not all, classical novae emit GeV gamma-rays during outburst, but the mechanisms involved in the production ofgamma-rays are still not well understood. ...We present here a comprehensive multiwavelength data set-from radio to X-rays-for the most gamma-ray-luminous classical nova to date, V1324 Sco. Using this data set, we show that V1324 Sco is a canonical dusty Fe ii-type nova, with a maximum ejecta velocity of 2600 km s−1 and an ejecta mass of a few . There is also evidence for complex shock interactions, including a double-peaked radio light curve which shows high brightness temperatures at early times. To explore why V1324 Sco was so gamma-ray luminous, we present a model of the nova ejecta featuring strong internal shocks and find that higher gamma-ray luminosities result from higher ejecta velocities and/or mass-loss rates. Comparison of V1324 Sco with other gamma-ray-detected novae does not show clear signatures of either, and we conclude that a larger sample of similarly well-observed novae is needed to understand the origin and variation of gamma-rays in novae.
ABSTRACT
The existence of a vast nova shell surrounding the prototypical dwarf nova Z Camelopardalis (Z Cam) proves that some old novae undergo metamorphosis to appear as dwarf novae thousands of ...years after a nova eruption. The expansion rates of ancient nova shells offer a way to constrain both the time between nova eruptions and the time for post-nova mass transfer rates to decrease significantly, simultaneously testing nova thermonuclear runaway models and hibernation theory. Previous limits on the expansion rate of part of the Z Cam shell constrain the inter-eruption time between Z Cam nova events to be >1300 yr. Deeper narrow-band imaging of the ejecta of Z Cam with the Condor Array Telescope now reveals very low surface brightness areas of the remainder of the shell. A second, even fainter shell is also detected, concentric with and nearly three times the size of the ‘inner’ shell. This is the first observational support of the prediction that concentric shells must surround the frequently erupting novae of relatively massive white dwarfs. The Condor images extend our Z Cam imaging baseline to 15 yr, yielding the inner shell’s expansion rate as v = 83 ± 37 km s−1 at 23 deg south of west, in excellent agreement with our 2012 prediction. This velocity corresponds to an approximate age of $t = 2672^{-817}_{+2102}$ yr. While consistent with the suggestion that the most recent nova eruption of Z Cam was the transient recorded by Chinese imperial astrologers in the year 77 bce, the age uncertainty is still too large to support or disprove a connection with Z Cam.
ABSTRACT
Just 10 recurrent novae (RNe) – which erupt repeatedly on time-scales shorter than one century – are known in our Galaxy. The most extreme RN known (located in the Andromeda galaxy), M31N ...2008-12a, undergoes a nova eruption every year, and is surrounded by a vast nova ‘super-remnant’, 134 pc in extent. Simulations predict that all RNe should be surrounded by similar vast shells, but previous searches have failed to detect them. KT Eri has recently been suggested to be a RN, and we have used the Condor Array Telescope to image its environs through multiple narrow-band filters. We report the existence of a large (∼50-pc diameter), H $\, \alpha$-bright shell centred on KT Eri, exactly as predicted. This strongly supports the claim that KT Eri is the 11th Galactic recurrent nova, and only the second nova known to be surrounded by a super-remnant. SALT spectra of the super-remnant demonstrate that its velocity width is consistent with that of M31-2008-12a.
Abstract
Nova V5856 Sagittarii is unique for having remained more than nine magnitudes above its pre-outburst brightness for more than 6 yr. Extensive visible and infrared (IR) spectra from the time ...of outburst to the present epoch reveal separate emitting regions with distinct spectral characteristics. Permitted emission lines have both broad and narrow components, whereas the forbidden line profiles are almost entirely broad. The permitted line components frequently display P Cygni profiles indicating high optical depth, whereas the broad components do not show detectable absorption. The densities and velocities deduced from the spectra, including differences in the O
i
λ
7773 and
λ
8446 lines, are not consistent with an ongoing wind. Instead, the prolonged high luminosity and spectral characteristics are indicative of a post-outburst common envelope that enshrouds the binary, and is likely the primary source of the visible and IR emission.
ABSTRACT Forbidden neon emission from jets of low-mass young stars can be used to probe the underlying high-energy processes in these systems. We analyze spectra of the jet of DG Tau obtained with ...the Very Large Telescope/X-Shooter spectrograph in 2010. Ne iii is clearly detected in the innermost 3″ microjet and the outer knot located at . The velocity structure of the inner microjet can be decomposed into the low-velocity component at km s−1 and the high-velocity component (HVC) at km s−1. Based on the observed Ne iii flux and its spatial extent, we suggest the origins of the Ne iii emission regions and their relation with known X-ray sources along the jet. The flares from the hard X-ray source close to the star may be the main ionization source of the innermost microjet. The fainter soft X-ray source at from the star may provide sufficient heating to help to sustain the ionization fraction against recombination in the flow. The outer knot may be reionized by shocks faster than 100 km s−1 such that Ne iii emission reappears and the soft X-ray emission at is produced. Velocity decomposition of the archival Hubble Space Telescope spectra obtained in 1999 shows that the HVC had been faster, with a velocity centroid of km s−1. Such a decrease in velocity may potentially be explained by the expansion of the stellar magnetosphere, changing the truncation radius and thus the launching speed of the jet. The energy released by magnetic reconnections during relaxation of the transition can heat the gas up to several tens of megakelvin and provide the explanation for on-source keV X-ray flares that ionize the neon microjet.
Abstract
Forbidden neon emission lines from small-scale microjets can probe high-energy processes in low-mass young stellar systems. We obtained spatially resolved Ne
iii
spectra in the microjets ...from the classical T Tauri Star Sz 102 using the Hubble Space Telescope Imaging Spectrograph at a spatial resolution of ∼0.″1. The blueshifted and redshifted Ne
iii
emission both peak in intensity within ∼0.″1 of the star and gradually decay along the flow outward to ∼0.″24. The spatial distribution and extent of the Ne
iii
microjet is consistent with a jet that is ionized close to the base and subsequently recombines on a longer timescale than the flow time. Ca
ii
H and K lines are also detected from the redshifted microjet with a line full-width at half-maximum of ∼170 km s
−1
, consistent with those of other forbidden emission lines, atop a 300 km s
−1
wide stellar component. The launching radius of the Sz 102 jet, inferred from the observed line centroids and the range of inclination angles and stellar masses from the literature, is on the order of ∼0.03 au. The possible proximity of the launching region to the star allows immediate ionization without distance dilution from the circumstellar ionization sources, most likely keV X-ray flares generated by magnetic reconnection events in the star--disk system, to sustain the observed Ne
iii
flux.
Stellar wind-emission features in the spectrum of eta Carinae have decreased by factors of 1.5-3 relative to the continuum within the last 10 years. We investigate a large data set from several ...instruments (STIS, GMOS, UVES) obtained between 1998 and 2011 and analyze the progression of spectral changes in direct view of the star, in the reflected polar-on spectra at FOS4, and at the Weigelt knots. We find that the spectral changes occurred gradually on a timescale of about 10 years and that they are dependent on the viewing angle. The line strengths declined most in our direct view of the star. About a decade ago, broad stellar wind-emission features were much stronger in our line-of-sight view of the star than at FOS4. After the 2009 event, the wind-emission line strengths are now very similar at both locations. High-excitation He I and N II absorption lines in direct view of the star strengthened gradually. The terminal velocity of Balmer P Cyg absorption lines now appears to be less latitude dependent, and the absorption strength may have weakened at FOS4. Latitude-dependent alterations in the mass-loss rate and the ionization structure of eta Carinae's wind are likely explanations for the observed spectral changes.
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