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 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:
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RA (ICRS) DE Designation(s)
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23 23 24.00 +58 48 54.0 Cas A = NAME Cassiopeia A
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 64 63 Physical parameters of 63 identified knots
table3.dat 71 2898 Observed NIR line parameters of knots
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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
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Bytes Format Units Label Explanations
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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)
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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 2010ApJ...711L.104D) and the extinction curve of the
Milky Way with RV=3.1 (Draine 2003ApJ...598.1017D 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.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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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)
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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 2006JPhB...39.2159F)
for [CI], Kelleher & Podobedova (2008JPCRD..37.1285K 2008JPCRD..37.1285K) for
[SiI], Tayal & Zatsarinny (2010, J/ApJS/188/32) for [SII],
Deb & Hibbert (2010ApJ...711L.104D 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.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 23-Oct-2017