Unveiling Vela – variability of interstellar lines in the direction of the Vela supernova remnant – III. Na D and Ca ii K (original) (raw)
Related papers
Monthly Notices of the Royal Astronomical Society, 2017
In a survey conducted between 2011 and 2012 of interstellar Na I D line profiles in the direction of the Vela supernova remnant (SNR), a few lines of sight showed dramatic changes in lowvelocity absorption components with respect to profiles from 1993 to 1994 reported by Cha & Sembach. Three stars-HD 63578, HD 68217 and HD 76161-showed large decrease in strength over the 1993-2012 interval. HD 68217 and HD 76161 are associated with the Vela SNR whereas HD 63578 is associated with γ 2 Velorum wind bubble. Here, we present high spectral resolution observations of Ca II K lines obtained with the Southern African Large Telescope towards these three stars along with simultaneous observations of Na I D lines. These new spectra confirm that the Na D interstellar absorption weakened drastically between 1993-1994 and 2011-2012 but show for the first time that the Ca II K line is unchanged between 1993-1994 and 2015. This remarkable contrast between the behaviour of Na D and Ca II K absorption lines is a puzzle concerning gas presumably affected by the outflow from the SNR and the wind from γ 2 Velorum.
Astrophysical Journal, 1998
The star HD72089 is located behind the Vela supernova remnant and shows a complex array of high and low velocity interstellar absorption features arising from shocked clouds. A spectrum of this star was recorded over the wavelength range 1196.4Å to 1397.2Å at a resolving power λ/∆λ = 110, 000 and signal-to-noise ratio of 32 by STIS on the Hubble Space Telescope. We have identified 7 narrow components of C I and have measured their relative populations in excited fine-structure levels. Broader features at heliocentric velocities ranging from −70 to +130 km s −1 are seen in C II, N I, O I, Si II, S II and Ni II. In the high-velocity components, the unusually low abundances of N I and O I, relative to S II and Si II, suggest that these elements may be preferentially ionized to higher stages by radiation from hot gas immediately behind the shock fronts.
Monthly Notices of the Royal Astronomical Society, 1999
We present ultra-high resolution (R < 10 6) observations of lines due to interstellar Na i D, Ca ii K, K i and Ti ii towards k Vel (HD 81188). Five velocity components are identi®ed in both Na i and Ca ii, and two in K i; an upper limit is recorded for Ti ii. The very high spectral resolution has enabled us to resolve fully the intrinsic interstellar line pro®les, and thereby obtain reliable measurements of the velocity dispersion parameters (b-values) for all identi®ed velocity components. By comparing the observed b-values for Na i and K i, which differ in mass by almost a factor of 2, it has been possible to derive the kinetic temperature (T k) and lineof-sight rms turbulent velocity (v t) simultaneously for the two clouds identi®ed in both elements. We obtain rigorous upper limits of 0.46 and 0.33 km s À1 for v t in these two clouds, which are de®nitely subsonic at the measured temperatures. The three-dimensional turbulent velocity (; 3 p´v t) is also almost certainly subsonic for both components, although it might just exceed the isothermal sound speed if the kinetic temperatures were close to the lower limits permitted by the line-pro®le analysis.
Far-Ultraviolet Spectral Images of the Vela Supernova Remnant
The Astrophysical Journal, 2006
We present far-ultraviolet (FUV) spectral-imaging observations of the Vela supernova remnant (SNR), obtained with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR) instrument, also known as FIMS. The Vela SNR extends ∼ 8 • in the FUV and its global spectra are dominated by shock-induced emission lines. We find that the global FUV line luminosities can exceed the 0.1-2.5 keV soft X-ray luminosity by an order of magnitude. The global O VI:C III ratio shows that the Vela SNR has a relatively large fraction of slower shocks compared with the Cygnus Loop.
The Astrophysical Journal, 2017
We present 888 visual-wavelength spectra of 122 nearby type II supernovae (SNe II) obtained between 1986 and 2009, and ranging between 3 and 363 days post-explosion. In this first paper, we outline our observations and data reduction techniques, together with a characterization based on the spectral diversity of SNeII. A statistical analysis of the spectral matching technique is discussed as an alternative to nondetection constraints for estimating SN explosion epochs. The time evolution of spectral lines is presented and analyzed in terms of how this differs for SNe of different photometric, spectral, and environmental properties: velocities, pseudo-equivalent widths, decline rates, magnitudes, time durations, and environment metallicity. Our sample displays a large range in ejecta expansion velocities, from ∼9600 to ∼1500 km s −1 at 50 days post-explosion with a median a H value of 7300 km s −1. This is most likely explained through differing explosion energies. Significant diversity is also observed in the absolute strength of spectral lines, characterized through their pseudo-equivalent widths. This implies significant diversity in both temperature evolution (linked to progenitor radius) and progenitor metallicity between different SNeII. Around 60% of our sample shows an extra absorption component on the blue side of the a H P-Cygni profile ("Cachito" feature) between 7 and 120 days since explosion. Studying the nature of Cachito, we conclude that these features at early times (before ∼35 days) are associated with Si II l6355, while past the middle of the plateau phase they are related to high velocity (HV) features of hydrogen lines.
The Local Interstellar Medium in Puppis‐Vela
The Astrophysical Journal Supplement Series, 2000
The first study of the local interstellar medium (LISM) toward Puppis-Vela (l = 245 • to 275 • , b = −15 • to +5 • , d < 200 pc) is presented in this paper. A study of the locations, sizes, and physical characteristics of local interstellar gas, i.e. "astronephography," is included, and relies upon the improved distance measurements provided by Hipparcos parallax measurements. All spectra of more distant sight lines contain absorption features due to intervening local gas, and more distant structures can only be studied accurately if components due to the LISM have been isolated. Towards this end, high resolution (R ≈ 95,000), high signal-to-noise (S/N ∼ 110 to 250) Na I λλ5889.951, 5895.924 spectra of 11 nearby stars in the direction of Puppis-Vela have been obtained with the Coudé Echelle Spectrograph on the 1.4 meter Coudé Auxiliary Telescope at the European Southern Observatory. Toward Puppis-Vela, absorption due to the Local Interstellar Cloud (LIC) was not observed, but components at three distinct velocities were found, and the extent of the local gas producing the features was estimated. The three components have the following locations and velocities: Component A-[l ≈ 276 • to 298 • , b ≈ −5 • to +4 • ], V helio = +6 to +9 km s −1 , and d ∼ 104 pc; Component B-[l ≈ 264 • to 276 • , b ≈ −7 • to +3 • ], V helio = +12 to +15 km s −1 , and d ∼ 115 pc; Component C-[l ≈ 252 • to 271 • , b ≈ −8 • to −6 • ], V helio = +21 to +23 km s −1 , and d ∼ 131 pc. The conclusions regarding the ultraviolet spectrum of γ 2 Vel (l = 263 • , b = −8 • , d = 258±35 pc) presented by Fitzpatrick & Spitzer (1994) were reexamined in light of this new LISM data, and the ambiguity in their conclusions about several absorption components is resolved. The stars in Puppis-Vela flank the region of the apparent extension of the Local Bubble (or Cavity) known as the β CMa tunnel, and measurements of the Na I column density towards the sample stars have been used to modify existing estimates of the extent of the tunnel. A compilation of all existing Na I observations of < 200 pc sight lines around the tunnel reveal that low column densities have been exclusively detected within l ≈ 210 • to 250 • , and b ≈ −21 • to −9 •. Near the Galactic plane, at latitudes −10 • < b < 0 • and d 150 pc, the tunnel is confined to l < 270 • , a lower longitude than was previously reported.
kappa Velorum: another variable interstellar sightline?
Monthly Notices of the Royal Astronomical Society, 2000
We present ultra-high-resolution R 900 000 observations of interstellar Na i and K i absorption lines towards k Vel (HD 81188) which show clear evidence for temporal variation between 1994 and 2000. Specifically, the column densities of K 0 and Na 0 in the main velocity component have increased by 40 and 16 per cent, respectively, over this period. Earlier work had suggested that this component actually consists of two unresolved sub-components; this result is confirmed here, and the overall line profile is found to be consistent with only one of these sub-components having increased in strength since 1994. We argue that this variation is consistent with the line of sight gradually probing a cold, dense interstellar filament of the kind recently proposed by Heiles to explain other observations of small-scale structure in the interstellar medium.
Using Line Profiles to Test the Fraternity of Type Ia Supernovae at High and Low Redshifts
The Astronomical Journal, 2006
Using archival data of low-redshift (z < 0.01; CfA and SUSPECT databases) Type Ia supernovae (SN Ia) and recent observations of high-redshift (0.16 < z < 0.64; ) SN Ia, we study the "uniformity" of the spectroscopic properties of nearby and distant SN Ia. We find no difference in the measures we describe here. In this paper, we base our analysis solely on line-profile morphology, focusing on measurements of the velocity location of maximum absorption (v abs ) and peak emission (v peak ). Our measurement technique makes it easier to compare low and high signal-tonoise ratio observations. We also quantify the associated sources of error, assessing the effect of line blending with assistance from the parametrized code SYNOW . We find that the evolution of v abs and v peak for our sample lines (Ca ii l3945, Si ii l6355, and S ii l l5454, 5640) is similar for both the low-and high-redshift samples. We find that v abs for the weak S ii l l5454, 5640 lines, and v peak for S ii l5454, can be used to identify fast-declining [∆m 15 (B) > 1.7] SN Ia, which are also subluminous. In addition, we give the first direct evidence in two high-z SN Ia spectra of a doubleabsorption feature in Ca ii l3945, an event also observed, though infrequently, in low-redshift SN Ia spectra (6/22 SN Ia in our local sample). Moreover, echoing the recent studies of Dessart & Hillier (2005a,b) in the context of Type II supernovae (SN II), we see similar P-Cygni line profiles in our large sample of SN Ia spectra. First, the magnitude of the velocity location at maximum profile absorption may underestimate that at the continuum photosphere, as observed for example in the optically thinner line S ii l5640. Second, we report for the first time the unambiguous and systematic intrinsic blueshift of peak emission of optical P-Cygni line profiles in Type Ia spectra, by as much as 8000 km s −1 . All the high-z SN Ia analyzed in this paper were discovered and followed up by the ESSENCE collaboration, and are now publicly available.
Variable interstellar lines in spectra of HD 73882
Publications of the Astronomical Society of the Pacific, 2013
We report a detection of variability in interstellar absorption lines of CaI at 4227 Å and FeI at 3860 Å in very high signal-to-noise ratio (>1000) UVES and MIKE spectra of HD 73882 (NX Vel) carried out with the aid of 8-m telescope UT2 at Paranal and 6.5-m Magellan Telescope Clay at Las Campanas Observatory, Chile. The spectra, acquired in 2006 January and 2012 January, respectively, clearly show that the intensity and profile shapes of the CaI and FeI lines had dramatically changed within the 6 year period. Other interstellar features, observed along the same line of sight, do not demonstrate strong changes. It is likely that a high velocity CaFe cloud obscured the star between the two observations.
The Astrophysical Journal, 1994
We have developed a grid of nonequilibrium of ionization (NEI) models that depends on the electron temperature and ionization time and that is suitable for use in Ðtting X-ray spectra. Using this grid, we have carried out a spatially resolved spectral analysis of a ROSAT Position Sensitive Proportional Counter (PSPC) observation of the northeast shock region of the Vela supernova remnant on an angular scale of 10@ (D1.0 pc at the distance of the remnant). The adopted model passes the s2 test at the 95% conÐdence level for 45% of the considered spatial bins, giving unexpectedly low values of the ionization time (log q D 0È1 yr cm~3). We discuss the possibility that this result may be due to a reduced contribution from a line emission, which may be related to the locking of metals in grains. We also Ðnd signiÐcant temperature gradients on the scale explored, and we argue that they are correlated to interstellar matter inhomogeneities encountered by the shock front. The emission from the remaining 55% of the bins is incompatible with the single-tau single-temperature NEI model, and a feasible description rests on the two-temperature collisional equilibrium of ionization model we have adopted in our previous analysis of the same data set. We tentatively interpret our results in terms of the superposition of shocks propagating in an inhomogeneous medium, which produces a multitemperature and multiÈionization stage plasma. Subject headings : ISM : individual (Vela supernova remnant) È ISM : structure È supernova remnants È X-rays : ISM