J/ApJS/260/34 NH3 transitions detections toward W51 IRS2 (Zhang+, 2022)
Three-month monitoring of the variability toward W51 IRS2 with ammonia, water,
and methanol transitions.
Zhang Y.-K., Chen Xi, Sobolev A.M., Shen Z.-Q., Li B., Zhao Z.
<Astrophys. J. Suppl. Ser., 260, 34 (2022)>
=2022ApJS..260...34Z 2022ApJS..260...34Z
ADC_Keywords: Star Forming Region; Molecular data; Radio lines; Masers;
Spectra, radio; Interstellar medium
Keywords: Interstellar masers ; Interstellar line emission ; Galactic center ;
Molecular clouds ; Molecular spectroscopy ; Star formation ;
Abstract:
A four-epoch monitoring program spanning ∼three months (from
2020-January-8 to April-7) for ammonia, water, and methanol
transitions toward the high-mass star-forming region W51 IRS2 was
conducted using the Shanghai 65m Tianma Radio Telescope with its
K-band (18-26.5GHz) receiver. In total, 33 ammonia transitions and
16 methanol transitions were detected toward the target at least once
during this monitoring program. Among them, 14 ammonia and 4 methanol
transitions show maser emission characteristics. Rapid variabilities
(including both increases and decreases) in the ammonia and methanol
transitions were detected from both maser and thermal emissions during
the three months of the monitoring. In addition, H2O masers with
obvious variability were also detected. The results of the rotation
diagram analysis for the ammonia and methanol quasi-thermal
transitions show the variations in their rotational temperatures
during the monitoring. The derived temperatures from the transitions
with larger upper energies (Eu/κ) generally decreased over the
whole monitoring period, from January 8 to April 7, but those with
smaller Eu/κ first increased from January 8 to April 1, then
rapidly decreased from April 1 to April 7. These findings support the
suggestion that an inside-out heatwave propagation in W51 IRS2 was
involved with the accretion burst over a short duration (only on the
order of months) and caused the drastic variability behaviors of the
different line transitions during high-mass star formation.
Description:
Observations of the NH3 inversion transitions at a frequency range
of 18.0-26.5GHz were carried out toward W51 IRS2 with the Shanghai 65m
Tianma Radio Telescope (TMRT) at four epochs: 2020 January 8,
mid-March (consisting of three days: March 14, 16, and 20), April 1,
and April 7. During these observations, all the NH3 transitions with
J≤11 were selected from the SPLATALOGUE database as target lines.
Objects:
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RA (ICRS) DE Designation(s)
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19 23 40.05 +14 31 07.1 W51 IRS2 = NAME W 51 IRS 2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 69 33 Details of the observed NH3 transitions
table2.dat 111 199 Line parameters of the quasi-thermal and maser
components in the detected NH3 spectra
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See also:
VIII/96 : 6-GHz methanol multibeam maser catalogue (Caswell+, 2010-12)
J/ApJ/692/973 : Protostars in Perseus, Serpens and Ophiuchus (Enoch+, 2009)
J/ApJS/206/22 : Newly EGOs from GLIMPSE II survey. II. MoC (Chen+, 2013)
J/ApJ/783/130 : Parallaxes of high mass star forming regions (Reid+, 2014)
J/MNRAS/439/2584 : Southern methanol masers at 36 and 44GHz (Voronkov+, 2014)
J/A+A/595/A27 : JVLA images of W51A (Ginsburg+, 2016)
J/ApJ/854/170 : Methanol (CH3OH) & OH masers in NGC 6334I (Hunter+, 2018)
http://splatalogue.online/ : Splatalogue database for astronomical spectroscopy
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Trans The observed NH3 (J,K) transitions
8- 17 F10.4 MHz Freq [18017.3/25715.2] Rest frequency
19- 25 F7.2 K Eu [23.3/1449.9] Upper level energy, Eu/K
27- 32 F6.2 D2 Smu2 [1.37/130.3] Transition strength, Sµ2 (1)
34- 43 A10 --- Obs Observation epoch(s) (2)
45- 54 A10 --- Det Detected epoch(s) (2)
56- 69 A14 --- Comm Comment (3)
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Note (1): The product of the total torsion-rotational line strength and the
square of the electric dipole moment for each transition, depending on
the data from the JPL catalog database.
Note (2): Epoch as follows:
1 = 2020 January 8
2 = 2020 March 20 (14 and 16)
3 = 2020 April 1
4 = 2020 April 7
Note (3): Summary of the transitions detected as follows:
maser = the transitions that show narrow maser spectral features;
maser? = the transition has narrow maser spectral features but with
a much lower S/N than the "maser" transitions;
thermal = the transitions that show broad quasi-thermal line profiles.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Trans Transition (J,K)
8- 8 A1 --- Abs [*] *=Detected in absorption on that date (1)
10- 18 A9 "Y/M/D" Date UT Observation date
20- 24 F5.2 km/s Vc-qt [49.4/68.2]? Centroid velocity,
quasi-thermal comp (2)
26- 29 F4.2 km/s e_Vc-qt [0.03/2.8]? Uncertainty in Vc-qt (2)
31- 31 A1 --- l_Tp Limit flag for Tp (3)
33- 37 F5.2 K Tp [0.03/22.81]? peak main-beam temperature
39- 43 F5.3 K e_Tp [0.01/2]? Uncertainty for Tp
45- 49 F5.2 km/s FWHM [2.7/27]? line width, full width at half-max
51- 54 F4.2 km/s e_FWHM [0.08/6.2]? Uncertainty in FWHM
56- 56 A1 --- l_W Limit flag on W (3)
58- 63 F6.2 K.km/s W [0.4/145]? Integrated intensity, main component
65- 68 F4.2 K.km/s e_W [0.07/2.3]? Uncertainty in W
70- 73 F4.1 --- tau [0.9/25.3]? optical depth (4)
75- 77 F3.1 --- e_tau [0.2/3.3]? Uncertainty in tau
79- 83 F5.2 km/s Vc-MF [47.35/72.56]? line centroid, maser feature (2)
85- 88 F4.2 km/s e_Vc-MF [0/0.5]? Uncertainty in Vc-MF (2)
90- 90 A1 --- l_Sp Limit flag on Sp (3)
92- 96 F5.2 Jy Sp [0.06/28.5]? Peak flux density
98-101 F4.2 Jy e_Sp [0.01/1.4]? Uncertainty in Sp
103-106 F4.1 km/s Vr-min [44.6/70.3]? Velocity range of
the narrow maser features, min
108-111 F4.1 km/s Vr-max [48.7/74.8]? Velocity range of
the narrow maser features, max
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Note (1): The NH3 transitions detected on that epoch are shown in absorption
(see Figure 2). Notably, line parameters are obtained after compensating
the absorption using the Gaussian fits for these transitions with
absorption features.
Note (2): When a transition is observed but not detected the Vc values are
taken from the closest observation having the target lines detected and
the uncertainty is set to null.
Note (3): When a transition is observed but not detected the 3σ RMS
value is recorded as an upper limit and the uncertainty is set to null.
Note (4): Determined from the five Gaussian component fits to the
quasi-thermal profiles.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 02-Aug-2022