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A keplerian-like disk around the forming o-type star afgl 4176

TL;DR: In this article, the Atacama Pathfinder Experiment (APEX) 12CO observations were used to uncover a Keplerian-like disk around the forming O-type star AFGL 4176.
Abstract: We present Atacama Large Millimeter/submillimeter Array (ALMA) line and continuum observa- tions at 1.2mm with 0.3′′ resolution that uncover a Keplerian-like disk around the forming O-type star AFGL 4176. The continuum emission from the disk at 1.21mm (source mm1) has a deconvolved size of 870±110AU × 330±300AU and arises from a structure 8M⊙ in mass, calculated assuming a dust temperature of 190K. The first-moment maps, pixel-to-pixel line modeling, assuming local thermodynamic equilibrium (LTE), and position-velocity diagrams of the CH3CN J=13–12 K-line emission all show a velocity gradient along the major axis of the source, coupled with an increase in velocity at small radii, consistent with Keplerian-like rotation. The LTE line modeling shows that where CH3CN J=13–12 is excited, the temperatures in the disk range from 70 to at least 300K and that the H2 column density peaks at 2.8×1024 cm−2. In addition, we present Atacama Pathfinder Experiment (APEX) 12CO observations which show a large-scale outflow from AFGL 4176 perpen- dicular to the major axis of mm1, supporting the disk interpretation. Finally, we present a radiative transfer model of a Keplerian disk surrounding an O7 star, with a disk mass and radius of 12M⊙ and 2000AU, that reproduces the line and continuum data, further supporting our conclusion that our observations have uncovered a Keplerian disk around an O-type star.

Summary (1 min read)

2.1. ALMA Observations

  • Calibration was carried out using the Common Astronomy Software Applications (CASA) version 4.2.1 via the delivered pipeline script.
  • The authors improved the resulting images by self-calibration of the continuum, and applied these solutions to the line data.
  • The continuum images were made using 1.4 GHz bandwidth of line-free channels across all spws.
  • Imaging was carried out using Briggs weighting with a robust parameter of 0.5.

2.2. APEX Observations

  • On-the-fly maps of 2.5 ′ ×2.5 ′ extent were taken in two perpendicular scan directions to reduce scanning artifacts.
  • The achieved rms in the spectra in the central part of the map is around 0.12 K.
  • The data reduction was performed within GILDAS/CLASS 7 .

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Johnston, KG, Robitaille, TP, Beuther, H et al. (6 more authors) (2015) A Keplerian-like
disk around the forming O-type star AFGL 4176. Astrophysical Journal Letters, 813 (1).
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arXiv:1509.08469v1 [astro-ph.SR] 28 Sep 2015
Preprint typeset using L
A
T
E
X style emulateapj v. 5/2/11
A KEPLERIAN-LIKE DISK AROUND THE FORMING O-TYPE STAR AFGL 4176
Katharine G. Johnston
1
, Thomas P. Robitaille
2
, Henrik Beuther
2
, Hendrik Linz
2
, Paul Boley
3
, Rolf Kuiper
4,2
,
Eric Keto
5
, Melvin G. Hoare
1
and Roy van Boekel
2
(Accepted September 30, 2015)
ABSTRACT
We prese nt Atacama Large Millimeter/submillimeter Array (ALMA) line and continuum observa-
tions at 1.2 mm with 0.3
′′
resolution that uncover a Keplerian-like disk around the forming O-type
star AFGL 4176. The continuum emission from the disk at 1.21 mm (source mm1) has a deconvolved
size of 87 0±110 AU × 330±300 AU and arises from a structure 8 M
in mass , calculated as suming
a dust temperature of 190 K. The first-moment maps, pixel-to-pixel line modeling, assuming local
thermodynamic equilibrium (LTE), and positio n-velocity diagra ms of the CH
3
CN J=13–12 K-line
emission all show a velocity gradient along the major axis of the source, coupled with an increase in
velocity at small radii, consistent with Keplerian-like rotation. The LTE line modeling shows that
where CH
3
CN J=13–12 is excited, the temperatures in the disk range from 70 to at lea st 300 K and
that the H
2
column density peaks at 2.8×10
24
cm
2
. In addition, we present Atacama Pathfinder
Experiment (APEX)
12
CO observations which show a large-scale outflow from AFGL 4176 perpen-
dicular to the major ax is o f mm1 , supporting the disk interpretation. Finally, we present a radiative
transfer model of a Keplerian disk surrounding an O7 star, with a disk mass and r adius of 12 M
and
2000 AU, that r e produces the line and continuum data, further supporting our conclusio n that our
observations have uncovered a K e ple rian disk around an O-type star.
Subject headings: radia tive transfer techniques: interferometric circumstellar matter stars:
formation stars : massive ISM: jets and outflows
1. INTRODUCTION
The process of star formation is often pictured as a
young star being fed by a disk formed as a result of
angular momentum conservation over a per iod of tens
of thousands to millions of years. Yet this pictur e has
been mainly derived from o bservations of disks that
have practically finished accreting. In actuality, it has
been confirmed only relatively recently that stable, ro-
tationally supported, Keplerian disks around low-mass
Class 0 /I protostar s exist at earlier times, when the
star and its disk is concea led deeply in an accreting
envelope (e.g., Brinch et al. 2007; Jørgensen et al. 2 009;
Tobin et al. 2012; Murillo et al. 2013).
The situation is even less clear when it comes to form-
ing massive s tars, which go on to reach a final mass of
8 M
and above. As they form so quickly (t
form
10
4
- 10
5
yr), they spend the entirety of their formation
still embedded in a surrounding envelo pe. Are these
protostars the high-mass equivalents of low-mass Class
0/I objects, and do they also have disks? Many of
the ene rgetic feedback mechanis ms associated with mas-
sive stars, such as radiation pressure and at later times
stellar winds and photo-io niz ation, would halt the vast
amount of accretion required to form these stars. In the-
1
School of Physics & Astronomy, E.C. Stoner Build-
ing, The University of Leeds, Leeds, LS2 9JT, UK;
k.g.johnston@leeds.ac.uk
2
Max Planck Institute for Astronomy, onigstuhl 17, D- 69117
Heidelber g, Germany
3
Ural Federal University, Astronomical Observatory, 51 pr.
Lenina, Ekaterinburg, Russia
4
Institute of Astronomy and Astrophysics, Eberhard Karls
University T¨ubingen, Auf der Morgenstelle 10, D- 72076
ubingen, Germany
5
Harvard-Smithsonian Center for Astrophysics, 60 Garden St,
Cambr idge, MA 02138, USA
ory, these ca n be bypassed by the existence of a disk
(e.g. Yorke & Sonnhalter 2002; Krumholz et al. 2009;
Kuiper et al. 2010, 2011), allowing the radiation pres-
sure, winds, or hot ionized gas to be channeled away
along the axis per pendicular to the disk, where densities
are lowe r.
Recent observations of early B-type (proto)stars have
responded to this prediction with detections of disk
candidates which have kinematics that appea r to be
dominated by the centr al protostar and are stable
(e.g. Johnston et al. 2011; anchez-Monge et al. 2013;
Cesaroni et al. 2014; Beltr´an et al. 2014). Yet the num-
ber of disks discovered so fa r only constitutes a hand-
ful (Cesaroni et al. 2007; Beltr´an et al. 2011), as many
of the observed rotating structures, instead referred to
as toroids, ar e too large and rotate too slowly to b e in
centrifugal equilibrium. Stepping up to O-type stars,
there are even fewer candidates (e.g., Wang et al. 2012;
Hunter et al. 2014; Zapata et al. 2015); in these cases the
detections are based on a velocity gradient across the
source and an outflow or jet that is projected perpendic-
ular to the candidate disk plane.
In this letter we present ALMA obser vations that
trace a Keplerian-like disk toward the infrared source
AFGL 4176, which co nstitutes the best observational ex-
ample of an O-type protostar with a disk to-date.
AFGL 4176 (G308.918+0.123, IRAS 133 95-6153) is a
forming massive star with coordinates 13
h
43
m
01
s
.69 -
62
08
51.3
′′
(FK5 J2 000), embedded in a star-forming
region with a total luminosity of 10
5
L
(d =
4.2 kpc, Boley et al. 2012; Green & McClure-Griffiths
2011). The source lies at the northern edge of an
H ii region (Caswell et al. 1992; Ellingsen et al. 2005;
Shabala et al. 2006) that peaks 4
′′
to the south o f
AFGL 4176, likely powered by another sta r of spectral

2 Johnston et al.
type O9. Four 6.7 GHz Class II methanol maser spots
with an extent of 840 AU at 4.2 kpc lie in close proxim-
ity to AFGL 417 6 along a line with position angle (PA)
-35
(Phillips et al. 1998). NH
3
observations have un-
covered that the star is embedded in a large-scale ro-
tating toroid with a radius of 0.7 pc (Johnston et al.
2014). The large-scale continuum emission at 1.2 mm
(Beltr´an et al. 2006) traces a dense core of 0.8 pc and
890 M
at 4.2 kpc, and knots of shocked H
2
emission
have been detected (De Buizer et al. 2 009), suggesting
the presence of an outflow. Boley et al. (2012) have mod-
eled the spectral energy distribution (SED) and mid-IR
interferometric observations of AFGL 4176, finding that
the latter required a non-s pherically-symmetric model
to adequately fit the data. They interpreted the mid-
IR visibilities as a combination of a disk-like structure
with radius of 660 AU at 4.2 kpc , inclination of 60
, and
PA=112
, and a spherically symmetric Gauss ian halo
with a FWHM of 60 0 AU (Boley et al. 2012, 2013). Fi-
nally, I le e et al. (2013) found that the 2.3µ m C O band-
head emission toward AFGL 4176 is consistent with the
inner 10 AU of a Keplerian disk.
2. OBSERVATIONS
2.1. ALMA Observations
We observed AFGL 4176 with the 12 m antenna array
of the Atacama Large Millimeter/submillimeter Array
(ALMA) during Cycle 1, under program 2012.1.00469.S
(PI Johnston). The observations were carried out o n
2014 August 16 a nd 17 in dual-polarization mode in
Band 6 (250 GHz or 1.2 mm) under good weather
conditions (precipitable water vapo r, PWV1.32 and
1.14 mm respec tively). AFGL 4176 was observed with
one pointing centered on 13
h
43
m
01
s
.08 -62
08
55.5
′′
(FK5 J2000). Two wide and two na rrow spectral win-
dows (spws) were observed with respective widths of
1.875 GHz and 468.750 MHz. The two wide spws were
centered at 240.541 and 254.043 GHz, while the two nar-
row spws were centered at frequencies of 239.072 and
256.349 GHz. The spectral res olution was 1129 kHz (1.41
and 1.33 km s
1
) and 282 kHz (0 .354 and 0 .330 km s
1
)
respectively. Thirty-nine antennas were included in the
array, of which 36 had useful data. Baseline lengths were
14.4 to 1210.8 m, providing a largest angular scale of
18
′′
. The primary beam size was 22.7 - 24.4
′′
. The
bandpass calibrators were J1617-5848 and J1 427-4206
and absolute flux calibrators were Titan and Ceres on
August 16 and 17 respectively. Phase/gain ca librators
were J1308-6707 and J1329-5608 for both days. The flux
calibration uncertainty was estimated to be .20%.
Calibration was carried out using the Common Astron-
omy Softwar e Applications (CASA) version 4.2.1 via the
delivered pipeline script. We improved the resulting im-
ages by self-calibratio n of the continuum, and applied
these solutions to the line data. The continuum images
were made using 1.4 GHz bandwidth of line-free channels
across all s pws. The central frequency of the combined
continuum emission is 247.689 GHz (1.210 mm). Imag-
ing was carried out using Briggs weighting with a robust
parameter of 0.5. The noise in the continuum image is
78 µJy beam
1
in a beam of 0.28
′′
×0.24
′′
, PA=-30.2
. In
this letter, we also present the detected K ladder transi-
tions of CH
3
CN J=13–12. The K=0 to 8 transitions were
13h43m01.5s02.0s
RA (J2000)
55" -62°08'50"
Dec (J2000)
mm1
mm2
mm3
mm4
mm5
mm6
mm7
mm8
m Jy beam
1
5000 AU
0
6
12
18
24
30
36
42
48
Figure 1. Continuum emission toward AFGL 4176 at 1.21 mm
observed with ALMA, in grayscale and contours (σ =
78µJy beam
1
× -5, 5, 10, 25, 50, 100, 200, 300, 400). The beam is
shown in the bottom left corner. The red cross shows the position
of the Class II methanol maser gr oup reported in Phi llips et al.
(1998) and the mm sources are labeled.
observed within the 239.072 GHz band. For the K=2 to
8 images presented below, the noise ranges between 3.4
and 6.2 mJy be am
1
in a beam of 0.30
′′
×0.28
′′
, PA=37.7
to 37.9
.
2.2. APEX Observations
We observed AFGL 41 76 with the Atacama Pathfinder
Experiment (APEX)
6
12 m antenna for program
M0020
89 during the night 2012 April 20–21 under very
good wea ther (PWV0.4 mm). The Swedish Hetero-
dyne Facility Instrument (SHeFi) APEX-2 receiver was
tuned to
12
CO(3-2) at 345.79599 GHz in the lower side-
band, providing a beam size of 18
′′
. On-the-fly maps o f
2.5
×2.5
extent were taken in two perpendicular scan
directions to re duce scanning artifacts. The XFFTS2
backend provided a channel separation of 0.1984 km s
1
.
The achieved rms in the spectra in the central part of
the map is around 0.12 K. The data reduction was per-
formed within GILDAS/CLASS
7
. Brightness tempera-
tures throughout this letter a re stated in main-bea m tem-
peratures (T
MB
).
3. RESULTS AND DISCUSSION
In Fig. 1 we present the 1.21 mm continuum emission
from the AFGL 4176 region. The emissio n is domi-
nated by mm1, with a peak position in the non-self-
calibrated image of 13
h
43
m
01
s
.693 -62
08
51.25
′′
(FK5
J2000), coincident with the position of AFGL 41 76 in
2MASS (with 0.1
′′
positional uncertainty
8
). Perform-
ing a gaussian fit to mm1, we determined a peak flux of
37±2 mJy beam
1
, an integrated flux of 50 ±4 mJy, a de-
convolved size of 0.21±0.03
′′
×0.08±0.07
′′
(870±110 AU
6
APEX is a collaboration between the Max-Planck-Institut f¨ur
Radioastronomie, the European Southern Observatory, and the
Onsala Space Observatory.
7
http://www.iram.fr/IRAMFR/GILDAS
8
http://www.ipac.caltech.edu/2mass/releases/allsky/doc/
sec1
6b.html#psrecptsour

A Keplerian-like disk around AFGL 4176 3
42m56s13h43m04s
RA (J2000)
-62°09'00" 08'00"
Dec (J2000)
-44 to -38 kms
1
-65 to -58 kms
1
K kms
1
0.5 pc
0
40
80
120
160
200
240
280
Figure 2. Large-scale bi polar outflow from AFGL 4176 seen in
12
CO J=3–2 with APEX. The total integrated emissi on is shown
in grayscale, and the integrated red- and bl ue-s hifted emission is
shown in contours at 40, 50, 60...90 % of the peak integrated fluxes
(11.5 and 24.9 K km s
1
resp ectively). Velocity ranges for integra-
tion of the red- and blue-shifted emission are shown in the bottom
right, and the beam in the bottom left. The cross and dashed line
mark the peak and PA of the continuum emission shown in Fig. 1.
×330±300 AU), and PA=59±17
. Using the equations
of Hildebrand (1983), a s well a s assuming 190 K (the av-
erage temperature of the disk derived from CASSIS LTE
line modeling below), a gas-to-dust ratio of 154 (Draine
2011), and a dust opacity at 1.21 mm of 0.24 cm
2
g
1
(Draine 2003a,b, with R
V
= 5.5), we de rive a gas mass
and peak column density of 8 M
and 8×10
24
cm
2
for
mm1. As well as a compact compo ne nt, mm1 includes
low-lying 5-10σ emission extending NW, perpendicular
to the major axis of mm1, that joins it to mm2. The
remaining mm sources lie in the NW and SE quadrants
around mm1, including two compact source s mm2 and
mm4 on opposite sides of mm1. Full obse rved proper-
ties of all detected 1.21 mm sources will be given in a
upcoming paper (Johnsto n et al., in preparation).
Figure 2 shows the integrated
12
CO J=3–2 emission
from the red- and blue-shifted high- velocity wings of the
bipolar outflow from AFGL 4176 observed by APEX,
overlaid upo n a
12
CO zero-moment map shown in
grayscale. The outflow lo bes are orientated roughly
NW-SE, perp endicular to the PA of the source mm1,
shown a s a dashed line in Fig. 2. This r elative geome-
try suggests mm1 is a disk driving the large -scale out-
flow see n in
12
CO.
The kinematics of the gas in mm1 traced by first- and
second-moment maps (intensity-weighted velocity and
linewidth fields r espectively) of CH
3
CN J=13–12 K=3
emission are shown in panels a) and b) of Fig. 3. The
velocity field of the K= 3 line in panel a) shows a clear
velocity gradient along the major axis of mm1, which
is also pre sent in lines K=2–8 and on arcminute scales
in NH
3
(Johnston et al. 2014). The velocity field shown
in Fig. 3 is similar to tha t expe c ted from disks in near-
Keplerian rotation (e.g. HD 100546 and TW Hya, re-
spectively Pineda et al. 2014; Hughes et al. 2011). For
instance, there is a quick change from blue- to red-s hifted
emission when cr ossing the minor axis of the source. In
addition, the emission in the most blue- and red-shifted
channels is found close to the continuum peak po sition,
whereas the lower-velocity gas is more extended. The
linewidths across mm1 in panel b) peak towards the con-
tinuum pea k, co nsistent w ith beam-averaging of high-
velocity red- and blue-shifted emission. There is e x-
tended CH
3
CN emission to the NW of mm1 with near-
systemic velocities (v
LSR
-52 km s
1
), as well as blue-
shifted gas associated with mm2, which would be con-
sistent with this source being associated with the blue-
shifted lobe seen in
12
CO.
Figure 3 panels c) through f) present the results of
modeling the CH
3
CN and CH
13
3
CN J=13–12 K-ladders
in the spectrum associated w ith each pixel, making a
map of excitation temperature (T
ex
), velocity (v
LSR
),
linewidth (v
FWHM
), and column density (N
mol
) across the
source. The modeling was carried out using CASSIS
9
and the JPL mo lecular spectroscopy database
10
, using
the Markov Chain Monte Carlo χ
2
minimization method
and assuming Local Thermodynamic Equilibrium (LTE).
Given N
mol
and T
ex
, CASSIS determines an optical
depth which is included in each model. We assume
a [
12
C/
13
C] abundance ratio of 60 (assuming the dis-
tance to the Galactic center is 8.4 k pc and thus a Galac-
tocentric distance to AFGL 41 76 of 6.6 kpc; Reid et al.
2009; Milam et al. 2005), a source size of 0.53
′′
from
the fitted size of the K=0,1 zero-moment map, and ini-
tial parameter ranges T
ex
= 50 350 K, v
LSR
= -57 -
47 k m s
1
, v
FWHM
= 0.5 10 km s
1
and N
mol
= 1×10
14
1×10
17
cm
2
. The resultant temperature shown in panel
c) peaks at the continuum peak position, and has val-
ues ranging between 74 and 29 4 K. There is also a sec-
ondary temperature peak toward mm2. Panels d) and
e) show similar res ults to the first- and second-moment
maps shown in panels a) and b), however an increase in
linewidth can be seen more clearly toward mm2. The
column density of CH
3
CN peaks at 2.8×10
16
cm
2
to-
ward the center of mm1, with a slight elongation along
the major axis. Using the assumed size above, and an
abundance of CH
3
CN of 10
8
(e.g. Gibb e t al. 2000;
Bisschop et al. 2007), this corre sponds to H
2
column and
volume densities of 2.8×10
24
cm
2
and >8×10
7
cm
3
re-
spectively.
Having established that a rotating structure, likely a
disk, surrounds AFGL 4176 mm1, we can compare it
with the geometry of the circumstellar material deter-
mined from modeling of o bservations from the MID-
infrared interferometric Instrument (MIDI; Boley et al.
2012, 2013). The PA of mm1 (60
) is not aligned
with the 112
determined fro m the MIDI visibilities. Al-
though these PA are not exactly orthogonal, these two
observations may be reconciled if the MIDI observatio ns
are instead tracing heated dust in the outflow c avity,
such as found for W33 A (de Wit et al. 2010). We also
note that although offset from the continuum peak of
mm1, the four Class II methanol maser spo ts detected
by Phillips et al. (19 98) shown in Figure 3 f) lie along a
line almost per pendicular to the disk.
To investigate the dynamics of mm1 further, we
9
CASSIS is developed by IRAP-UPS/CNRS
(http://cassis.irap.omp.eu)
10
http://spec.jpl.nasa.gov

4 Johnston et al.
(a)
V
LSR
(kms
1
)
2000 AU
13h43m01.8s 01.6s
-62°08'50.0"
50.5"
51.0"
51.5"
52.0"
50
51
52
53
(b)
V
FWHM
(kms
1
)
2000 AU
13h43m01.8s 01.6s
2
4
6
8
(c)
T
ex
(K)
2000 AU
13h43m01.8s 01.6s
100
150
200
250
(d)
V
LSR
(kms
1
)
2000 AU
13h43m01.8s 01.6s
-62°08'50.0"
50.5"
51.0"
51.5"
52.0"
50
51
52
53
(e)
V
FWHM
(kms
1
)
2000 AU
13h43m01.8s 01.6s
2
4
6
8
(f)
N
mol
/
10
16
(cm
2
)
2000 AU
13h43m01.8s 01.6s
1
2
3
Dec (2000)
RA (2000)
Figure 3. Panels a) and b) show first- and second-moment maps of the CH
3
CN J=13–12, K=3 emission from AFGL 4176 mm1 in
colorscale. Panels c) through f) s how the results of the CASSIS pixel-to-pixel spectrum fitting. Continuum emission (starting at 10 σ)
similar to that shown in Fig. 1 is overplotted as contours in all panels except d), which show s the integrated K=3 emission at 10, 30, 50,
70 and 90% of the peak. The beam is shown in the bottom left corner of all panels. Panel f) shows the positions of the C lass II methanol
masers from Phillips et al. (1998).
present position-velocity (PV) diagrams of the CH
3
CN
J=13–12 K=2,4,6, and 8 lines in Fig. 4 panels a) to d),
along a cut centered on the continuum peak position of
mm1, with width=1
′′
and PA=61.5
, which was the av-
erage PA of the emission in the CH
3
CN J=13–12 K=4,
5 and 6 lines, which had good signal-to-noise and were
not contaminated by envelope emission.
The PV diagrams of the K=2,4 and 6 lines exhibit
the “butterfly” shape expec ted from a Keplerian-like
rotation c urve that increases in velocity close to the
central object, and is more extended c lose to the sys-
temic velocity. It bears close resembla nc e to the PV-
diagrams observed toward the forming early B-type star
IRAS 20126+4014, which has a disk in Keplerian-like
rotation (Cesaroni 20 05; Cesaroni et al. 2014), as well
as the forming O-type stars NGC 6334 I(N) SMA 1 b
and IRAS 16547-4247 (Hunter et al. 2014; Zapata et al.
2015, respe c tively). The velo city gradient of the K-lines
becomes steeper at higher values of K, thus the more-
excited lines that trace hotter ga s closer to the c e ntral
object also trace higher veloc ities, which is expected from
Keplerian-like rotation.
Interestingly, the PV-diagrams of the lower-K lines
shown in Fig. 4 are asymmetrical about the systemic
velocity, with the blue-shifted emission being brighter.
This is not observed however in the K=7,8 lines. A sim-
ilar blue-as ymmetry is seen in the PV-diagrams of the
low-excitation K-lines of CH
3
CN J=12–11 observed by
Cesaroni et al. (2014) and Hunter et al. (2014), whereas
the high-excitation lines are either symmetric al or ex-
hibit a red-asymmetry. The CH
3
CN J=19–18 K=2 PV
diagram of G35.03+0.35 HMC A als o shows this blue-
asymmetry (Beltr´an et al. 201 4). This has bee n sug-
gested to be due to an asymmetric disk structure, how-
ever the fact that s o ma ny objects exhibit the same fea-
tures in their PV-diagrams suggests this is more likely
due to a radiative transfer e ffect and/or a geometry that
is present in all sources.
To check whether a Keplerian-disk model is consis tent
with our obse rvations, we ran a grid of self-consistent gas
and dust radiative transfer models, where the line and
continuum radiative transfer were performed using the
codes Mollie (assuming LTE, Keto & Caselli 2010) and
Hyperion (Robita ille 2011), using the Milk y Way dust
properties from Draine (2003a,b) with R
V
= 5.5, respec-
tively. To fit the models to the line and continuum obser-
vations, we fit the profiles of the co ntinuum and CH
3
CN
J=13–12 K=2-8 emission collapsed along the major and
minor axes, as well as the integrated spe ctra for the lines.
The models were convolved to the observed beam before
fitting.
Panels e) to h) of Fig. 4 show the CH
3
CN J=13–12
PV diagrams for a model which provides a good fit to
the line and continuum data. The model consists of a
Keplerian flared disk of radius 2000 AU (the inner ra-
dius is set to be the dust sublimatio n radius, in this case
31.3 AU), total gas mass 12 M
, with a surface density
decreasing as r
1.5
and an inc lination of 30
. The scale-
height of the disk is given by z = 6.7 (/100AU)
1.29
AU
where is the cylindrical ra dius and the constants were
determined in order for the disk to be in hydrostatic
equilibrium. The model includes a rotationally-flattened

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Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "A keplerian-like disk around the forming o-type star afgl4176" ?

The authors present Atacama Large Millimeter/submillimeter Array ( ALMA ) line and continuum observations at 1. 2mm with ∼0. In addition, the authors present Atacama Pathfinder Experiment ( APEX ) CO observations which show a large-scale outflow from AFGL4176 perpendicular to the major axis of mm1, supporting the disk interpretation. Finally, the authors present a radiative transfer model of a Keplerian disk surrounding an O7 star, with a disk mass and radius of 12M⊙ and 2000AU, that reproduces the line and continuum data, further supporting their conclusion that their observations have uncovered a Keplerian disk around an O-type star.