J/ApJ/837/118 NIR knots in the Cas A supernova remnant (Lee+, 2017)
Near-infrared knots and dense Fe ejecta in the Cassiopeia A supernova remnant. Lee Y.-H., Koo B.-C., Moon D.-S., Burton M.G., Lee J.-J. <Astrophys. J., 837, 118-118 (2017)> =2017ApJ...837..118L (SIMBAD/NED BibCode)
ADC_Keywords: Supernova remnants ; Spectra, infrared ; Radial velocities ; Extinction ; Interstellar medium Keywords: infrared: ISM; ISM: individual objects: Cassiopeia A; ISM: supernova remnants; line: identification; methods: statistical Abstract: We report the results of broadband (0.95-2.46µm) near-infrared spectroscopic observations of the Cassiopeia A supernova remnant. Using a clump-finding algorithm in two-dimensional dispersed images, we identify 63 "knots" from eight slit positions and derive their spectroscopic properties. All of the knots emit [FeII] lines together with other ionic forbidden lines of heavy elements, and some of them also emit H and He lines. We identify 46 emission line features in total from the 63 knots and measure their fluxes and radial velocities. The results of our analyses of the emission line features based on principal component analysis show that the knots can be classified into three groups: (1) He-rich, (2) S-rich, and (3) Fe-rich knots. The He-rich knots have relatively small, ≲200km/s, line-of-sight speeds and radiate strong He I and [FeII] lines resembling closely optical quasi-stationary flocculi of circumstellar medium, while the S-rich knots show strong lines from O-burning material with large radial velocities up to ∼2000km/s indicating that they are supernova ejecta material known as fast-moving knots. The Fe-rich knots also have large radial velocities but show no lines from O-burning material. We discuss the origin of the Fe-rich knots and conclude that they are most likely "pure" Fe ejecta synthesized in the innermost region during the supernova explosion. The comparison of [FeII] images with other waveband images shows that these dense Fe ejecta are mainly distributed along the southwestern shell just outside the unshocked 44Ti in the interior, supporting the presence of unshocked Fe associated with 44Ti. Description: We carried out NIR spectroscopic observations of Cas A using TripleSpec (wavelength coverage from 0.94 to 2.46um at a spectral resolving power of R∼2700) mounted on the Palomar 5m Hale telescope. On 2008 June 29 and August 8, we obtained spectra at eight slit positions along the main ejecta shell (see Figure 1). In 2005 August 28 and 2008 August 11, we performed NIR imaging observations for the remnant using the Wide-field Infrared Camera (WIRC) attached to the Palomar 5m telescope. Objects: ------------------------------------------------------- RA (ICRS) DE Designation(s) ------------------------------------------------------- 23 23 24.00 +58 48 54.0 Cas A = NAME Cassiopeia A ------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 64 63 Physical parameters of 63 identified knots table3.dat 71 2898 Observed NIR line parameters of knots
See also: VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006) J/ApJ/428/693 : Rosette Nebula and Maddalena Cloud structures (Williams+ 1994) J/ApJ/456/234 : Cas A radio knots spectral indices (Anderson+ 1996) J/ApJ/613/343 : Cas A knot and filament proper motions (Delaney+, 2004) J/A+A/484/755 : Oxygen recombination lines from Cas A knots (Docenko+, 2008) J/ApJS/179/195 : A catalog of outer ejecta knots in Cas A (Hammell+, 2008) J/ApJS/188/32 : Breit-Pauli transition probabilities for SII (Tayal+, 2010) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1 I1 --- Slit [1/8] Slit number 3- 4 A2 --- Knot Knot number 6 A1 --- f_Knot [e] Flag on Knot (1) 8- 9 I2 h RAh Hour of right ascension (J2000) 11- 12 I2 min RAm Minute of right ascension (J2000) 14- 18 F5.2 s RAs Second of right ascension (J2000) 20 A1 --- DE- Sign of declination (J2000) 21- 22 I2 deg DEd Degree of declination (J2000) 24- 25 I2 arcmin DEm Arcminute of declination (J2000) 27- 30 F4.1 arcsec DEs Arcsecond of declination (J2000) 32- 35 F4.2 arcsec Size [1.7/9.8] Size along the slit length 37- 38 A2 --- Type Knot type (2) 40- 43 F4.1 mag Av [3.3/15.4] Visual extinction (3) 45- 47 F3.1 mag e_Av [0/3.6] Av uncertainty 49- 53 I5 km/s RV [-2234/1924] Radial velocity 55- 56 I2 km/s e_RV [2/20] RV uncertainty 58- 61 I4 10-20W/m2 FeII [34/4959] [FeII]1.644um Flux; in 10-17erg/s/cm2 units 63- 64 I2 10-20W/m2 e_FeII [3/13] FeII uncertainty (4)
Note (1): e = Knot 4 in Slits 5 and 6 has been identified as a single knot by Clumpfind, but a detailed inspection revealed that each are composed of two (A and B) components almost coincident both in space and velocity. Note (2): Knot type as follows: He = He-rich knot (7 occurrences) S = S-rich knot (45 occurrences) Fe = Fe-rich knot (11 occurrences) Note (3): Visual extinction derived from the flux ratio of [FeII] 1.257 and 1.644um. We adopted the intrinsic [FeII] line ratio of 1.36 (Deb & Hibbert 2010ApJ...711L.104D) and the extinction curve of the Milky Way with RV=3.1 (Draine 2003ApJ...598.1017D ; see Section 4.1 for more details). Note (4): The uncertainty in parenthesis is the 1σ statistical error by a single Gaussian fitting, and does not include the absolute photometric error which is roughly 20% or less.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1 I1 --- Slit Slit Number 3- 4 A2 --- Knot Knot Number 6- 35 A30 --- Line Line identification (Transition: lower-upper) 37- 43 F7.5 um lamAir [0.9/2.3] Rest Wavelength in air 45- 48 F4.1 0.1nm FWHM [3.4/37]? FWHM of lines in Angstroms 50- 52 F3.1 0.1nm e_FWHM [0.1/10]? The 1σ uncertainty in FWHM 54- 58 I5 10-20W/m2 Flux [3/13213]? Observed flux in 1E-17 erg/s/cm2 60- 62 I3 10-20W/m2 e_Flux [1/903]? The 1σ uncertainty in Flux (1) 64- 71 A8 --- Note Note (2)
Note (1): The uncertainty is 1σ statistical error from a single Gaussian fitting, and does not include the absolute photometric error which is roughly 20% or less. The uncertainty of undetected lines was derived from the background rms noise around the wavelength. The emission lines falling in the bad atmospheric transmission window (e.g., [FeII] lines near 1.80um) have much higher uncertainty in flux due to low signal-to-noise ratios. Note (2): In the case of the lines which were contaminated by nearby lines of similar wavelengths either from the knot itself or from other knots, we carried out a simultaneous Gaussian fitting with possible constraints ("LINE-FIX" keyword in Note), e.g., by fixing their wavelengths and/or line widths based on the parameters of well-isolated lines, by fixing their intensities if they can be predictable theoretically (Froese Fischer (2006JPhB...39.2159F) for [CI], Kelleher & Podobedova (2008JPCRD..37.1285K) for [SiI], Tayal & Zatsarinny (2010, J/ApJS/188/32) for [SII], Deb & Hibbert (2010ApJ...711L.104D) for [FeII]). "OH-CONT" keyword in Note represents the line which was significantly contaminated by nearby bright OH airglow emission lines so their true uncertainty could be much larger than what we measured from a single Gaussian fitting.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 23-Oct-2017
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