星形成ゼミ
担当：SFN#345 24-29
2021/10/22
総研大 D2 竹村英晃

SFN#345 24-29
24. Physical Properties and Real Nature of Massive Clumps in the Galaxy

25. Discovery of a Highly Collimated Flow from the High-Mass Protostar
ISOSS J23053+5953 SMM2
26. Dynamical effects of the radiative stellar feedback on the H I-to-H2
transition
27. Characterization of the dust content in the ring around Sz 91: indications
for planetesimal formation?
28. Signatures of UV radiation in low-mass protostars I. Origin of HCN
and CN emission in the Serpens Main region

29. The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages(ASHES). IV. Star formation signatures in G023.477

arXiv:2108.08981v1 [astro-ph.GA] 20 Aug 2021

Physical
Properties
Accepted XXX. Received
YYY; in original form ZZZand Real Nature of Massive Clumps
in the Galaxy

•
•
•
•
•
•

ABSTRACT
Zu-Jia Lu, Veli-Matti Pelkonen, Mika Juvela, Paolo Padoan, Troels Haugbølle, Åke Nordlund

Systematic surveys of massive clumps have been carried out to study the conditions leading to the formation of massive
stars. These clumps are typically at large distances and unresolved, so their physical properties cannot be reliably derived fromthe observations alone. Numerical simulations are needed to interpret the observations. To this end, we generate synthetic
Herschel observations using our large-scale star-formation simulation, where massive stars explode as supernovae driving theinterstellar-medium turbulence. From the synthetic observations, we compile a catalog of compact sources following the exact
same procedure as for the Hi-GAL compact source catalog. We show that the sources from the simulation have observational
properties with statistical distributions consistent with the observations. By relating the compact sources from the synthetic
observations to their three-dimensional counterparts in the simulation, we find that the synthetic observations overestimate theclump masses by about an order of magnitude on average due to line-of-sight projection, and projection effects are likely to beeven worse for Hi-GAL Inner Galaxy sources. We also find that a large fraction of sources classified as protostellar are likely to
be starless, and propose a new method to partially discriminate between true and false protostellar sources.
Key words: MHD – radiative transfer – methods: numerical – stars: formation – catalogues
大質量クランプ（大質量星形成領域）のサーベイ観測が行われてきたが、距離が遠いため分解できず、物理量はよく分かっていない。
1 INTRODUCTION
we compile the first synthetic catalog of massive clumps that can be
観測のみでは限界があるため、数値シミュレーションを行う。
compared statistically to the Hi-GAL compact source catalog, based
Massivestars are essential constituents of the ecosystem of galaxies,
3D
MHDシミュレーション＋Herschelの模擬観測を行い、Herschelの観測結果（Hi-GAL）の結果と比較した。
on a star-formation simulation of a 250 pc region of the ISM driven
driving the thermodynamical and chemical evolution of their interby supernova (SN) explosions.
模擬観測の結果から同定したコンパクトな構造の質量は、視線方向に射影する効果により、1桁程度質量を過大評価している。
stellar medium (ISM). Understanding their formation process is aUsing earlier evolutionary stages of the same simulation, we haveprerequisite
for modeling Galaxyの天体ではより質量を過大評価しているかも。
the evolution of galaxies and investigating•
Hi-GALのInner
previously
shown that SNe alone can drive the observed turbulence
the high-redshift universe. A complete theory of star formation is notin MCs (Padoan et al. 2016a; Pan et al. 2016) and can explain bothProtostellarに分類されていた構造の中にstarlessが多く混ざっていた。
available yet, massive-star formation being perhaps the main hurdle
the formation and dispersion of MCs (Lu et al. 2020). The star forto overcome. An important limitation in the study of massive stars
mation rate per free-fall time in the clouds was also found to beis the difficulty to test our theoretical models against observational
consistent with the observations (Padoan et al. 2017). The simulaHi-GALのサンプルは高空間分解能では、fragmentationしているはずなので、今後ALMAで観測していく必要がある。
data, because massive stars are more rare and shorter lived than lowtion was then used to study the formation of massive stars in Padoanmass stars. Regions of massive star formation tend to be at relatively
et al. (2020), where it was also shown that observations could grossly
large distances, obscured by high extinction levels, and confused byoverestimate the mass of protostellar
cores, depending on distancecomplex gas and stellar dynamics, as massive stars form in stellar
https://arxiv.org/pdf/2109.01243.pdf

シミュレーション（3D MHD + AMR）•

𝐿!"# = 250 pc（グリッド：0.24 ‒ 0.0076 pc）、 𝑀!"# = 1.9×10$ 𝑀⨀。

•

乱流の起源はSNのみ (Padoan et al. 2016a; Pan et al. 2016)。

•

初期条件：𝑛&,( = 5 cm)* 、𝑇( = 10+ K、𝐵( = 4.6 µG（自己重力なしで45 Myr計算）••

70 µm, 160 µm, 250 µm
𝑡 = 34.2 Myr, 𝐷 = 2 kpc

SNをランダムに起こす（6.25 SNe Myr-1）。

𝑛 > 10$ cm)* など (Haugbølle et al. 2018) の条件でsink（星）を作り、7.5 M◉を超え
かつ星の寿命 (Schaller et al. 1992) を迎えたものたところでSNを起こす。
•星の質量とモーメント、1051 ergのエネルギーをガウシアン分布でその場に残す (Padoan et al. 2016a)。

•4283個の星（>2 M◉）が形成され、~415回のSNeが発生。
•

大質量側（ >8 M◉ ）の質量分布は、SalpeterのIMFを再現。

模擬観測•

自己重力を入れてから15.4、23.3、34.2 Myr後のスナップショットをHershcelで模擬観測（70、160、250、350、500 μm）。
•

距離は2、4、8、12 kpc→各波長ごとに36マップ

構造同定•

Hi-GAL (Elia et al. 2017, 2021) と同じ手法を適用。
•

CuTEx (Moli- nari et al. 2011)：画像の2階微分を用いて構造同定（Curvature-based source detection）

Real Nature of Massive Clumps

3

Hi-GALカタログと本研究のカタログでの物理量の比較•観測（Hi-GAL）と模擬観測からそれぞれ同定した構造の物理量は似た分布を持っている。→詳細な比較を行える。

Real Nature of Massive Clumps

Protostellar の割合

半径

質量

温度

Figure 4. Source classification and derived source parameters as a function of
distance. Top panels: fraction of protostellar sources in the synthetic catalog(solid line) and in the Hi-GAL catalogs (dashed lines) for the Outer Galaxy(left) and the Inner Galaxy (right). Second row: median values of the synthetic
source diameters, separated into starless (red) and protostellar (blue) sources.
Error bars are between the 2.5 and 97.5 percentiles. The median values for
the Hi-GAL sources are shown by the dashed lines, while the shaded regions
correspond to the same percentile range as for the error bars. Third row: thesame as the second row of panels, but for the source mass derived from theSED fitting. Fourth row: the same as the previous row, but for the source
temperature.

7

discussed in § 6.1 must be even larger in the Inner Galaxy survey than
実線：本研究、網掛け：Hi-GAL
in the synthetic observations. Finally, the bottom
panels of Figure 4
show that the observed clump temperatures are well reproduced by
8the synthetic
Z.-J. Luet al.
catalog,
except for slightly larger values in the case of
半径
質量
温度
protostellar sources at 2 and 4 kpc in the Outer Galaxy, and at all distances in the Inner Galaxy. This temperature difference is discussed
below in the context of Figure 5. The temperature of starless sources
is instead perfectly reproduced in both median values and dispersion
at all distances for both the Outer and the Inner Galaxy.
Figure 5 shows the probability distribution of the clump diameters(left panels), clump masses (middle panels), and clump temperatures(right panels) for starless and protostellar synthetic sources (solidline histograms), compared with the same distributions for the HiGAL sources (shaded-area histograms) in the Outer Galaxy (upper
panels) and in the Inner Galaxy (lower panels). All Hi-GAL sources
with distances between 1.5 and 13.5 kpc are included in the shadedarea histograms. Because the number of synthetic sources decreases
with distance approximately at the same rate as in the Outer Galaxy
catalog, the histograms from the synthetic catalog in the upper panels
are computed using the actual number of sources extracted at eachdistance, and then normalizing the total number of synthetic starlesssources to the same total number of observational starless sources,
and using the same normalization factor for the synthetic protostellar
clumps, too. In the case of the comparison with the Inner Galaxy(lower panels), the number of the synthetic sources is first multiplied
by a factor (3/2 kpc) 2 /2, for distances 3 > 2 kpc (and left unchanged
for sources at 2 kpc), to approximate the nearly constant number ofsources in the Hi-GAL Inner Galaxy catalog at distances between 2•and本研究のカタログ、Hi-GALカタログはともに距離に応じて同じ割合でサンプル数
125.kpc.
Afterthis distributions
normalization
the totalmasses,
numberandof temperatures for the starless (red solid line) and protostellar (blue solid line) sources
FigureUpperpanels:of bythe distance,source diameters,fromthe synthetic
catalog,
comparedto the sourcesfrom the
Hi-GAL Outersynthetic
sources
has beennormalized
by the ratioof observed
and Galaxy catalog (red and blue bars) in the distance interval between 1.5 and 13.5 kpc.
The
numberof synthetic
sources(bothand protostellar)
is normalized
by the ratio of Hi-GAL and synthetic starless sources. The vertical dashed andsyntheticstarless
sources.
Thus,
thestarlessarea below
the histogramsofが減っている。
dottedlinesandare observed
the medianstarlessvalues sources
for the synthetic
and Hi-GAL
catalogs,
synthetic
are the same,
while theareas respectively. Lower panels: the same as the upper panels, but comparing with the
Hi-GAL
Inner
Galaxy catalog.
To approximate
thereflectdistanceof the Hi-GAL sources in the Inner Galaxy, the number of synthetic sources at distancesthehistogramsof protostellar
sourcesthedistribution
actual ratios•3below
本研究のカタログのstarlessとprotostellarの数をそれぞれの距離にあるHi-GALカ
2 /2.
> protostellar
2 kpc is scaleda factor(3/2 kpc)
ofto bystarless
sourcesin boththe synthetic and Hi-GAL
catalogs. The vertical dashed and dotted lines are the median values
タログのサンプル数に規格化している（今後のプロットも）。
of the synthetic and Hi-GAL catalogs, respectively.
nessAsofshown
our stellar
mass
As 5,
mentionedin §good
2, theagreestellarcase of protostellar sources. In both Hi-GAL catalogs, the medianby theleft distribution.
panels of Figure
there is very
mass
the simulationis consistent
withwith
Salpeter’s
mass-size relations have nearly the same slope as Larson’s masmentdistribution
between thein synthetic
and Hi-GAL
sources
respect IMF
to(Salpeter
1955)
above ⇠in8both
M ,thebutmedianis incomplete
lowersize relation (solid line), corresponding to roughly constant surface
the source
diameters
valuesatandthemasses
shapes (andofnothestars
below ⇠distributions.
2 M are included
as stellarinsourcesin theradiative
density (Larson 1981). This slope is well reproduced in the synthetic
probability
The difference
the shapeof thehistransfer
the andlower
distances,
70 `m
flux
of mostcatalog as well.
togramscalculation).
between the At
Inner
Outer
Galaxythe
is dueto thedifferent
distance
more uniform
disstarsin thedistributions
range ⇠ 2 of8theM sources.
would Thebe detectedin the distanceobservations,
All the mass-temperature contour plots and median relations from

Hi-GALクランプと本研究のクランプの質量

Figure 6. Left four panels: mass versus diameter and mass versus temperature for starless (upper panels) and protostellar (lower panels) synthetic sources(solid contour lines). The black line is Larson’s mass-size relation, " (r) = 460 M (r/pc) 1.9 (Larson 1981). Source number density isocontours representing
the starless and protostellar sources from the Hi-GAL Outer Galaxy catalog are also displayed with dashed lines. The number densities have been computed
subdividing the area of the plot with a grid of 70 ⇥ 70 cells in logarithmic intervals. Once the global maximum of both distributions in the same panel (starlessor protostellar) has been found, the plotted contours are chosen to show the number density of 5%, 20% and 70% of the maximum, as in Figure 7 of Elia et al.
(2017). Right four panels: the same as in left four panels, but comparing with the sources from the Hi-GAL Inner Galaxy survey. In this case the number ofsynthetic sources at distances 3 > 2 kpc has been rescaled by a factor (3/2 kpc) 2 /2, to mimic the distance distribution of the sources in the Inner Galaxy, as in
Figure 5.

•

視線方向の密度プロファイル（シミュレーション結果）。
•

密度のピークをもつmainのクランプの他にも複数のクランプが存在する。

•

星がmainのクランプに付随している（左）こともあれば、そうではない場合（右）こともある。

105

105

star in column
star in clump

104

100

10

2

•

10

1

質量を過大評価している。

100

Z.-J.Mmain
Lu :et79.40,
al. Mall : 1613.20, Nc : 68
10 1
Mtot : 1719.81, MSED : 1037.00
diameter (the size on the plane of the sky). The position of the
0
50
100
150
200
250 maximum
0 density is50
100vertical transparent
150
200 in Figure250
shown by theline
7,
Lbox [pc]Lbox [pc]whose thickness corresponds to the diameter of the synthetic source
and thus
main
Wea also
defineas independent
3Dthe
Figure 7. Density profile along the line of sight for two example sources (the sametwo asofinthe
Figure3):3D
oneclump.
source has
dominant
clump(left panel) andclumpsall othermaximathanhighest
1% ofdensity
theother has many clumps of approximately the same peak density (right panel). The
red verticallinedensity
shows thepositionwithof thevalue
main larger
clump (the•t=34.2 Myrでの密度分布。
absolute
maximumthat defines
the main
3D clump(see the horizontalpeak), with the thickness of the line corresponding to the source diameter (we assumethatthe 3D clump
has the same
diameteras the corresponding
source).
The open cyan diamonds are the stars located inside the main clump. The open red
circles
are thelocated inare
theassumed
column ofsourcefootprint,
but outsidedashedline).
Allstars
3D clumps
tothe
have
a sizein the direction• The
若い星は高密度領域に分布している。
of the dominant clump.
green dashed horizontal line shows the 1% of the maximum
density,which
is minimum
density diameter
we have chosen
to define secondaryof the lineof sight
equal
to the source
as well.
clumps.
With these definitions of main and secondary 3D clumps, we can•
進化が進んだ星は高密度領域（原始星コア）に付随せず、ランダムに分布
then associate three different mass values to each line of sight, thetotal mass of the column, "tot , the sum of the 3masses of all clumps,
6.1 Observational versus
Intrinsic Clump Massmean density around the star in a (0.12 pc) volume. While in theするようになる。
"all , and the mass of the main clump, "main , and compare them with
example dominated by the main 3D clump (left panel) one star isthe mass of the corresponding synthetic source, "SED . In the twofound inside the mainclump,and several
more in its
vicinity, only11
Figure 7 shows the density profile along the lines of sight of two examples
Real
NatureofinMassive
Clumpsof Figure 7, themain
3D clump
left panel>the8thevalueM<has
5a massM
are found in the line of sight
of
the
other
(right◉ example
sources of similar mass (618 and 1037 M ) at 12 kpc, both classified " two stars
=
305.7
M
,
approximately
half
of
the
estimated◉mainpanel) and at relatively low densities, and none inside the main 3D
as protostellar in the synthetic catalog, chosen to be an example of a source
mass, "SED , while the main 3D clump in the right panel has aclump.
line of sightdominatedby aagerealclump (left panel) and of a line of 1 massstellar
<3D
1 Myr
5 Myr
> 5 Myr"main = 79.4 M , approximately 13 times
smaller than "SED .
103sight without a dominant 3D clump (right panel). The gas density is
profilesshown within Figure
7 arefor all
TheDensity
comparison
oflike"allthose
and "
"SED
for computed
all the sources
maincomputed within a column of size equal to the source diameter. The in our
the catalog
sources isinshown
our synthetic
catalog,
and
are
then
used
to
identify
in Figure 8, where the black solid line marks
open cyan diamonds mark the positions of stars located inside the thethe
main 3Drelation.
clump The
corresponding
to fits
eachto synthetic
source.
The
one-to-one
least-squares
the medianvalue of210星近傍
main 3D clump, while the open red circles are for the stars located in each
main
3Dtwo
clump
in eachline of ofsight
is defined
as intheFigurefractionof themassesas a function"SED
are shown
8 asofthe column of the source footprint, but outside of the main 3D clump. dashedthe corresponding
columnat theresult
highestdensitymaximumand dotted lines.
The centered
most strikingof thiscomparison
The y-axis coordinate of the diamonds and circles corresponds to the is thatand with
along the line
sight
equal
to thesynthetic
source" a sizeoverestimatesthe oftrue
massof themain
3D clump,
Mmain : 305.71, Mall : 653.55, Nc : 13
Mtot : 717.21, MSED : 618.48

10

N

10 1

101

100

SED

星近傍（各時間ごと）
10 3 10 2 10 1 100

101

102

103

104

105

"main , by a factor greater than 10, on average (dashed contour lines
MNRAS 000, 1–17 (2021)
and dotted least-squares fit). Because the median
relation given by(0.587±0.020)
the fit is rather shallow, "main = (0.230 ± 0.014)"SEDfor

10 3 10 2 10 1 100

101

観測では視線方向のemission
をすべて足し合わせるため、

102

103

104

105

10 3 10 2 10 1 100

101 (0.838±0.015)
102 103 104

3the Outern [cm] Galaxy and "main = (0.137 ± 0.009)"SED

105

(the

•

密度も過大評価している。
all clumps
main clump

103

Mall, Mmain [M ]101

MSEDとmainのクランプの質量。

102

101

100

Outer Galaxy

10 1
103

Mall, Mmain [M ]

10

•

103

n [cm 3]n [cm 3]103
2star in column

104

102

101

100

Inner Galaxy

10 1
100

101

102

MSED [M ]103Galaxy’s distance distribution shown in the upper panel). However,there is also a considerable overlap between the two types of sources.
To partially separate true from false protostellar sources, we propose
to separate the protostellar sources in two groups using theas due to protostellar
medianrelation for the true sources (cyan line). We first obtain an•
Protostellar（70μm検出あり）のサンプルには原始星が付随しているものと、そうではない“誤検出”が含まれている。
e two denser peaks in3
3
analytical
fit to the cyan line for the Outer Galaxy distance distribut ⇠ 10 cm , can be•
真のProtostellarの70μmの超過を温度の関数でフィットすることで、真のProtostellarの同定条件を設定。
tion,
nsity distribution andthe density threshold
2877
367
+
+ 1.3 ,
(6)
Outer:
Inner:
70,ob / 70,gb =d thus to discriminate
15()/10 K)()/10 K) 5

do not correspond too completely random

Protostellar クランプの同定

101
0.4

Protostellarでは、 MSED/Mmain ~4であり、 70 μmの超過からサンプルを分
MNRAS 000, 1–17 (2021)
類した場合でも、似た傾向が得られている。

0•Real Nature of Massive Clumps

0.0

Inner Galaxy

103

0.8

0.6

102
101

0.4

100
0.2

10 1
10 2
10

15

20

25

T [K]

30

35

0.0
40

Ntrue/Ntot

103

Mmain [M ]

104

102

starless
Outer Galaxy

Falsehigh 70µm excess

True

13
104
103

101

102

100

N

10 2

Protostellarはstarlessに比べて射影の影響を受けにくい。

101

10 1
103

100

102

Inner Galaxy

101

102

100

103

104
103

101

102

100

101

10 1
100

101 102 103
MSED [M ]100

101 102 103
MSED [M ]100

101 102 103
MSED [M ]100

101 102 103
MSED [M ]10 1 100 101 102 103
MSED/Mmain

100

N

0.2

10 1

F70,ob/F70,gb•

Mmain [M ]10

Ntrue/Ntot

F70,ob/F70,gb

and for the Inner Galaxy case,an be partially differ•上の条件よりも超過が大きい場合には、平均のprotstellarの検出率はouterとinnerで64%と66%なのに対し、超過が小さい
on purely observable
2051
365
+
+ 0.5 ,
(7)
m excess ontheir tem70,ob / 70,gb =場合にはそれぞれ14%と21%になる。
()/10 K) 15 ()/10 K) 5
the synthetic sources,
m excess and temperwhich is shown by the solid black lines in Figure 10. The dashedduces well that of theblack lines connecting the diamond symbols show the ratio between𝐹
he ratioof the 70 `mtrue protostellar 𝑁
sources
total protostellar sources found above
78, :;<=>?@AB:C
A>G=,and
H>:A:<A=II@>`m flux, 70,gb , thatthe analytical fits. The values of this ratio are shown in the y-axis
𝑁A:A@I,78,fluxes
D>@E;:FE
fit of𝐹theat theon the right-handside of H>:A:<A=II@>the plots. The lower black dotted lines,
0 shows that the temconnecting the circle symbols,
1.0 show the same ratio for sources below
True protostellar
protostellar
sources
the analytical Outer
fit to themedian line. One
see that, in the case of the104
Galaxy• canStarlessのサンプルでは、M
SED>>Mmain（ MSED/Mmain ~20）。
False
protostellar
as approximately
the
Outer
Galaxy,approximately
0.8 80% of the protostellar sources are true
103
i-GAL sources in theones in the approximate temperature range between
21 K and
33 K,
•
False
protostellarでも同様。
ith the Inner
Galaxy,while below the lines the fractionof true protostellar sources is always
102
0.6

arXiv:2109.06793v1 [astro-ph.GA] 14

Nicolaus Copernicus Astronomical Center, ul. Rabiańska 8, 87-100 Toruń, Poland
University of Le Havre, Laboratoire Ondes et Milieux Complexes, UMR CNRS 6294,75 Rue Bellot, 76600 Le Havre, France
12
Univ Rennes, CNRS, IPR (Institut de Physique de Rennes) – UMR 6251, F-35000 Rennes, France
11

Signatures of UV radiation in low-mass protostars

Received March
2021; accepted
September13, 2021
I. Originof19,HCN
and
CN
emission in the Serpens Main region••

Agnieszka Mirocha, Agata Karska, Marcin Gronowski et al.
ABSTRACT

Context. Ultraviolet radiation (UV) influences the physics and chemistry of star-forming regions, but its properties and significancein the immediate surroundings of low-mass protostars are still poorly understood.
Aims. We aim to extend the use of the CN/HCN ratio, already established for high-mass protostars, to the low-mass regime to trace
and characterize the UV field around low-mass protostars on ⇠ 0.6 ⇥ 0.6 pc scales.
Methods. We present 50 ⇥ 50 maps of the Serpens Main Cloud encompassing 10 protostars observed with the EMIR receiver at the
IRAM 30 m telescope in CN 1-0, HCN 1-0, CS 3-2, and some of their isotopologues. The radiative-transfer code RADEX and thechemical model Nahoon are used to determine column densities of molecules, gas temperature and density, and the UV field strength,
G0 .
Results. The spatial distribution of HCN and CS are well-correlated with CO 6-5 emission that traces outflows. The CN emission isextended from the central protostars to their immediate surroundings also tracing outflows, likely as a product of HCN photodissociation. The ratio of CN to HCN total column densities ranges from ⇠1 to 12 corresponding to G0 ⇡ 101 103 for gas densities andtemperatures typical for outflows of low-mass protostars.
Conclusions. UV radiation associated with protostars and their outflows is indirectly identified in a significant part of the Serpens
Main low-mass star-forming region. Its strength is consistent with the values obtained from the OH and H2 O ratios observed with
Herschel and compared with models of UV-illuminated shocks. From a chemical viewpoint, the CN to HCN ratio is an excellent
tracer of UV fields around low- and intermediate-mass star-forming regions.
Key words. astrochemistry – stars: formation – ISM: molecules – ISM: individual objects: Serpens Main – ISM: jets and outflows–Submillimeter: ISM

小質量星形成領域（Serpens Main）において、分子組成や温度へのUVの影響を調べた。
• Introduction
大質量星形成領域では観測例があり (Cesaroni 2005;cal
Zinnecker2007)、CNとHCNの比がUVの有無を調
1.
conditions &andYorkechemicalcomposition in star-forming regions
dependonthecharacteristicsof the above processes.
べるのによく使われる手法のひとつ (Doty & Neufeld 1997; Stäuber et al. 2005)。
The formation of low-mass stars is associated with many physThe importance of UV radiation for star formation was iniical
The inside-out collapse of dense cores is ac- tially considered only in the context of massive stars, where the• phenomena.
UV（X線）によってHCNがCNに電離され、CNの電離よりも10倍速く進む。→CN/HCNが大きくなる。
companied by the ejection of bipolar outflows and the formation central stars are the main source of UV photons from early stages
10個の原始星をCN、HCNなど（IRAMof embedded disks (e.g. Frank et al. 2014; 30
Li etm）で観測し、RADEX、Nahoonを用いてUV強度などを求めた。
al. 2014). Ul- (Cesaroni 2005; Zinnecker & Yorke 2007). In dense star-forming
traviolet (UV) radiation can be produced in mass accretion on environments, the far-UV radiation is revealed by the chemithe central object or bow shocks, and it irradiates the outflow cal composition of the material, since it dissociates and ionizes
cavities in the envelopes (Spaans et al. 1995; van Kempen et al. molecules and atoms with ionization potentials below 13.6 eV
2009a; Visser et al. 2012; Drozdovskaya et al. 2015). The physi- (Benz et al. 2016). More energetic photons are easily absorbed
in the surrounding interstellar medium (Draine 2003). Among?
the most useful diagnostics of UV radiation is the ratio of CN to
Corresponding author: Agata Karska
e-mail: agata.karska@umk.pl
HCN (Doty & Neufeld 1997; Stäuber et al. 2005). In the pres-http://arxiv.org/abs/2109.06793v1

観測結果

HCNはCO（アウトフロー）に沿って分布し、A. Mirocha et al. 2021: Signatures of UV radiation around low-mass protostars

CNは原始星に付随している傾向がある。

A. Mirocha et al. 2021: Signatures of UV radiation around low-mass protostars

Fig. 3: Line profiles of CO 6-5, C34 S 3-2, CS 3-2, H13 CN 2-1, H13 CN 1-0, HCN 1-0 and CN 1-0 lines at the protostellar position
Ser SMM4 (left) and the associated outflow position no. 3 (right). Blue vertical lines show the main line component, and grey lines
show the hyperfine splitting components. The maps in Figure 2 show the sum of all hyperfine components detected in the spectra of
HCN and CN.
and outflow positions nr 1, 4, and 5, exceeding 70% of the total
profile in HCN and 58% in CS. In fact, these high fractions ofline emission in the wings are upper limits, because the opacitye↵ects decrease the emission primarily in the source positions.
In case of the weaker lines like CN, the fraction of wing versus on-source emission might be slightly lowered due to a limited signal-to-noise ratio of the spectra, which might not recover
the wings at full. Higher signal-to-noise observations of rare isotopologue lines as well as CN would be needed to fully recover
the on-source and wing emission.
The shapes of line profiles clearly indicate that the emission
in various species is detected in di↵erent physical components ofthe protostellar systems. For the forthcoming analysis, we willconsider the emission in the line wings alone and in the fully
integrated profiles separately.

A. Mirocha et al. 2021: Signatures of UV radiation around low-mass protostars

Table 1: Properties of targeted protostars in the Serpens Main region

3.3. Line ratios

In this section, we calculate molecular line ratios at protostar andselected positions in the Serpens Main region separately for the

fully6-5integrated profiles and for the line wings. We discuss (i) the
Fig. 2: Integrated
maps of HCN
1-0 (upperTleft panel),(upperOther
right panel),
Source intensity
R.A.
Dec.
LbolCS 3-2
Class
namesCN 1-0 (bottom left panel) and CObol
ratios of di↵erent isotopologues, constraining the line opacities,(bottom right panel) toward the Serpens Main star-forming
regionshown in contours and colors. Black triangles show the positions(J2000.0)(J2000.0)(K)(L)
and (ii) the ratios of di↵erent species, reflecting their di↵erencesof protostars (see Table 1) and blue crosses show the outflow positions selected for analysis (see Table 3). Solid lines show outflow
SMM
18 (black;29 50.0Yıldız
+01
152015)20.3 and 37
115.2
0
FIRS1,
EC41,
in spatial extent and relative abundances.
directions
from1CO 6-5
et al.
CO 3-2(blue; Dionatos
etSer-emb6,
al. 2010). The
centerof theBolo23
maps (0,0) corresponds
h
m
0
1
1
1
s.6, 30
2 4918
12 57.8levels 34
7.2 (6 K0km s Ser-emb4,
Bolo28to (↵, )SMM
= 18 29+0100.5
15 2000.+01
5. Contour
start at 20), 10 (3 K
km s ), 7 (3.5 K km s ) andArticle
70 number, page 6 of 32
SMM
3 steps
18 29
13 59.2
7.1CN, CS
0 and COSer-emb26,
Bolo26(14 K kms 1 ) withof 59.6
10 , 3 +01, 3.5
and 50 35, for HCN,
respectively.

3.3.1. Ratios of different isotopologues

The line ratio of the same transition of two isotopologues is a
tracer of line opacity of the more abundant species, assumingthat the emission in the other isotopologue is optically thin. We
calculate line opacities of HCN 1-0 and CS 3-2 lines both at the
protostellar and outflow positions using (Goldsmith et al. 1984;
Mangum & Shirley 2015):
T HCN
⌫HCN
=
T H13 CN
⌫H13 CN!2

X[HCN] 1
X[H13 CN]

exp( ⌧HCN )
,
⌧HCN

(1)

where Xi and T i refer to the abundance and antenna temperatureof the isotopologue, and the same excitation for both isotopologues is assumed. We adopt an abundance ratio of HCN and
H13 CN following the standard interstellar ratio of 12 C/13 C of 68(Milam et al. 2005), and 20 for the CS and C34 S abundance ratio(Tercero et al. 2010), and assume that both isotopologues arise
from the same physical region, described by the excitation temperature, T exc , and in local thermodynamic equilibrium (LTE).
Optical depths at the protostellar positions range from ⇠2.3
to 12.8 for HCN and from ⇠0.3 to 4.4 for CS when the emission from the entire profile is considered (see Table E.3). At theoutflow positions, the optical depths are ⇠4.9-8.0 for HCN and⇠0.6-4.9 for CS. These values are in fact lower limits, becauseline profiles of HCN and CN show self-absorption toward many

SMM 4
18 29 57.0 +01 13 11.3
68
5.1
ISer-emb22, Bolo25
SMM 5
18 29 51.4 +01 16 38.3 151
3.7
I
Ser-emb21, EC53, WMW24, Bolo22
emissionSMM
in linein 57.8
the close+01
vicinityof Ser532
SMM143.1
is
InI the caseof Ser SMM4
(Figure3), the SVS20S,
emission inBolo
the line
6 wings
18 29
14 05.3
Ser-emb30,
EC90,
WMW35,
28
much weakercannotbe assigned
3-2 is 61% of the total profile at the protostellar
SMMthan
8 that18 of
30CN,
01.9which+01
15 09.2
15 to the0.2 wings0 of CSBolo30
self-absorption
the envelope.
emission
72% at theoutflowWMW23,
position. Similar
SMM 9of material
18 29 in48.3
+01 16 Low
42.7HCN33
11.0 position
0 andSer-emb8,
ISO241,
Bolo22characterisFig. 4: Emission in the line wings of HCN 1-0, CN 1-0, CS 3-2 and CO 6-5 toward Ser SMM1 (blue and red contours). The
might be rather related to the presence of large cavities around tics is seen in HCN line wings (48% and 68%, respectively).
SMM1周辺では、CNに比べてHCNが弱い。
SMM
10
18
29
52.3
+01
15
48.8
79
7.1
I
Ser-emb12,
WMW21,
Bolo
23
velocity ranges used to calculate the integrated intensities are provided in Appendix D. Black and green lines correspond to outflow
Ser SMM1, where ionizing radiation is capable of photodissoci- In contrast, CN 1-0 is detected mostly at source velocity, withdirections in CO 3-2 and CO 6-5 (the same as in Figure 2).
SMM
12
18
29
59.1
+01
13
14.3
72
10.0
I
Ser-emb19,
Bolo28ating HCN (Hull et al. 2016, Hull et al. 2017). A full analysis of 40% of emission in the line wings. Among all 15 positions, ex-RADEX for nH = 105 cm 3 and T kin = 50 K for a range of SMM9, and to a lesser extent toward Ser SMM8 and SMM10.
line intensity ratios (orange line). The observed line intensity ra- The former source drives a large outflow, where bright emission
CNとHCNの柱密度の比を求める。
tio is shown as a rectangle: light green color corresponding to in HCN likely results from its high abundance in the warm gas
the values observed at the protostar position, blue color for the (similarly to o↵-source position 3). The latter sources are charac8 color
8
weak
emission in general (Figure 2).
outflow
positions and dark green
for both regions. Column terized6 by•
HNCの柱密度を10cm-2 に固定し、CNの柱密度を10cma-2veryから
10molecular
cm-2 まで変化させる。
Ser
SMM8
is
a
low
luminosity
sources(Lbol of 0.2 L , see Table
density ranges are marked with black and navy emdashed lines
46 1), which-3
is located on the map edge in CO 6-5. Ser SMM10 is
温度 Tandは 50 -positions,
100 K、数密度nH は 10 - 10 cm の範囲で変化させる。
kin outflow
for• protostars
respectively.
associated with CO 6-5 peak, but is clearly very weak in both
CN and HCN.
Table 3: Model-dependent column density ratios of CN to HCN
The median value of the CN to HCN intensity ratio at theA&A proofs: manuscript no. a
at protostar and o↵-source
positions
柱密度比の計算結果
protostellar positions is 0.63 ± 0.19. Taking into account the
輝線強度比
emission in the line wings, the ratio is slightly lower and equals
In su
nH2
T kin NCN /NHCN NCN /NHCN
CN / IHCN
0.40 ± 0.18. It is Igenerally
consistent with the ratios measured
and CN3(cm ) (K) Protostars O↵-sourcefor each source using the full profile. The ratio calculated for the
influence
10450
1.57-5.55
0.85-3.79
selected o↵-source positions equals 0.43 ± 0.18 and 0.20 ± 0.18,
their rati
104
100 1.40-4.98
0.76-3.40
for the full profile and wings, respectively.
104
200 1.33-4.70
0.72-3.21
The CN/HCN intensity ratio for
the Class 0 protostars is
原始星
4
10
300 1.32-4.66
0.71-3.18
観測結果 3.3.2. Ra
0.61 ± 0.23 and for the Class I protostars is 0.67 ± 0.17, indicat104
400 1.45-5.13
0.78-3.50
ing that the evolutionary stage does not strongly a↵ect the meaLine rati
104
500 1.56-5.53
0.85-3.77
sured ratios. A slightly higher CN/HCN ratio for Class I protolocal abu
stars is consistent with increasing opening angles of the outflows
105
50
1.85-6.55
1.00-4.67
sity ratio
for more evolved sources and larger areas a↵ected by UV radia105
100 1.87-6.23
1.01-4.52
Prototion (see Discussion). The opacity e↵ects overestimate the ratioアウトフロー
105
200 2.01-7.12
1.09-4.86
theimpaof CN and HCN, and could have a slightly stronger impact on
105
300 2.14-7.60
1.16-5.18
east subc
5
the more massive envelopes of Class 0 sources (Section 3.3.1). (Off-sourse)
10
400 2.22-7.87
1.20-5.37
close to S
105
500 2.27-8.02
1.23-5.47
outflows
10650
2.52-8.93
1.37-6.10
Figure C
106
100 2.84-10.04 1.54-6.85
4. Analysis
is on the106
200 3.17-11.22 1.72-7.65
average oIn this section, we calculate column densities of the molecules
柱密度比o↵-sourc
106
300 3.33-11.80 1.80-8.05
with the radiative-code RADEX (van der Tak et al. 2007) and
106
400 3.01-10.67 1.63-7.28
NCN with/ NHCN The
Fig.
The ratio
to HCN column
densities
obtained
compare them tothe5:results
fromoftheCN
chemical-code
Nahoon,run
6
10
500 2.75-9.73
1.49-6.64
53
for ndensities
cm UV
and
T kin =fields.
50 K for a range of SMM9, a
H = 10 and
for a set of gas RADEX
temperatures,radiationline intensity ratios (orange line). The observed line intensity ra- The form
tio is shown as a rectangle: light green color corresponding to in HCN
protostars (Mottram et al. 2014), we find optical depth of CS 3-2 4.1. Column densitiesof observed
molecules
observations
the values
at from
the protostar
position, blue color for the (similarly
132line as 2.1, assuming column densities of 5 ⇥ 10 cm . Using
outflow positions and dark green color for bothregions. Column terized b•
柱密度比（CN/HCN）は、原始星の位置で1.3‒
11.8、アウトフローの位置（Off-sourse）で0.7
‒
8.1。
In
case
of
optically
thin
lines
and
LTE
conditions,thecolumna revised collisional rates for HCN adopted from Mullins et al.
density ranges are marked with black and navy emdashed lines Ser SMM
level of aandgiven
molecule,
Nu , canbe calcu1), which
2016, the optical depth calculated for HCN 1-0 is 2.9, assuming density of the upper
for protostars
outflow
positions,
respectively.
associatecolumn densities of 3 ⇥ 1014 cm 2 . This value is in agreement lated using Equation 2, where = 8⇡k/hc3 is a constant equal
CN and H
with the optical depth calculated from F=2!1 to F=1!1 ratio. toR 1937 cm 2 , W is the integrated intensity of the emission line
Table
Model-dependent
columnratios of CN to HCN
Similar optical depths (within a factor of 2) are found for gas ( T mb dV), A isthe 3:
Einsteincoefficient and⌫ is density
the transition
The m
at protostar
andando↵-source
positionstemperatures of 300 K and number densities of 104 cm 3 .
frequency between
the upper
lower level
expressed in GHz

輻射輸送（RADEX）

A&A proofs: manuscript no. amirocha

化学モデル（Nahoon） 柱密度比を使って、G0の値を求める。

A&A proofs:
amirocha at 50 K
Table 4: Dominant processesin CNmanuscriptand HCNno.chemistry

Molecule•

物理状態とUVの強度から、分子の存在量を求めるコード。

•

UV（星形成）なしで各分子のアバンダンス比が安定するまで
CN
A. Mirocha et al. 2021: Signatures of UV radiation around low-mass protostars
計算し、その後UVを入れて計算。

初期条件に至るまでの各分子の存在比の時間進化

星形成開始

nH = 104 cm-3
T = 10 K
Av = 5 mag

HCN

Table 4: Dominant processes in CN and HCN chemistry at 50 K

Weak UV fields
Medium UV fields
Strong UV fields
CN、HCNが関係する反応
1
1(G0 = 10 3 Weak
10 1UV) fields(G0 = 10
10UV
) fields(G0 =Strong
101 UV106fields)
Molecule
Medium3
1
1
1
Destruction(G0 = 1010 )(G0 = 1010 )(G0 = 101 106 )O + CN ! N + CO
CN + h⌫ !Destruction
C+N
CN + h⌫ ! C + N
CN + N !OC+ +
N!
!N
+ CO
CN
+ h⌫
!C+N
CN + h⌫ ! C + N
2 N + CO O + CN CN
Production
CN + N ! C + N2
O + CN ! N + CO
N + CH ! H + CN
N + C2 ! Production
C + CN
HCN+ + e ! H + CN
CN+CH
! H + CN H + CN+ N!+CN
C2 !
C ++ CNe +!CN
H + CN
CNC+ + e N
!+C
+
CN
+
H
N +HCNCH !+ H+++++ CH ! H + +
CNC
+
e
!
C
+
CN
H
+
CN
!
CN
+
H
N
N + C2 ! C + CN
H + CN ! +CN + H CN+
N + C2 ! C + CN
N +HC+2 CN
! C!
+ CN
CN + HN + C2 ! C + CN
Destruction
Destruction+++
HCN + C+HCN! H++CCNC
HCN
CNC+ h⌫+!h⌫H!+HCN++ + C ! H+!H
+ CNC
HCN + C +!
H + CNC+ HCNHCN
+ CN
+
+
+
+
HCN + H HCN! H++HHNC! H + HNC
HCN + h⌫ HCN! H++h⌫CN! H + CN
Production
HCN
Production
+
NH
+ CH
H+
C + HCNHCNH
HCNH
+ HCN
N + CH2 !
+ HCN
H + CCN
!CCN
C +!
HCN
+ e+ +!e H!+HHCN
2 ! H + HCN+
H +CCCN! C + HCN
+He +!
H + HCNH + CCN
H + CCN+ HCN
H + CCN !
+ HCN
HCNH+HCNH+e !
HCN! C!+ CHCN+
! H + HCN
HCNH+ + HCNH
e ! H++eHCN

UV放射を考慮したときの、CNとHCNの柱密度比
value of G0 . The ratio increases with G0 until it equals

value of G0 . The ratio increases with G0 until it equals ⇠sequently, the NCN /NHCN decreases for higher G0 . S
sequently,
the Nperformed
for higher
G0 . Sim
CN /NHCN decreases
culationsat 300 K show
a very similarp• culations
ガス密度はKristensen
etsimilar
al. patte
at 300 K show a very
Fig.performed
F.1).
Fig. F.1). The N /N
CN HCN ratios obtained from observations
The
NCNtransfer/NHCN models
ratios obtained
observationsan(2012)の値を使用。
tiveare ⇠ 1 from12 (see
Section 4.1).
gnatures of UV radiation around low-mass protostars
modelsmodels
are consistentcolumndens
tive transfer
are ⇠ with
1 the
12 observed(see Section
4.1).
C
3
5 cm
-3 fields
CNtoHCN
for with
UV
that are 10
largerdensity
than tmodelsareconsistent
the observed
column
•
n
=10
のとき
H
Fig. 6: Time evolution of CN
3interstellar
value(Figure7 (red line), HCN (blue line) and
CN to HCN
for UV
fieldsthat8).areThe
10observations
larger thanarethea
星形成開始後10yr のアバンダンス比（tent value
with models
withsignificantly
lower UVCS (blackline) abundances obtainedwith Nahoon astrochemical Av＝5 ）interstellar(Figure8).
Theobservations
are fields
also
3
5.5
2
G10
‒ 10
。 lowertimes theaverageinterstellar
UV UV
field.fields,
For throcode with initial parameters of nH = 104 cm 3 , T = 10 K, AV = Fig. 7: Contour plot of Nahoon sets of models of CN/HCN abun0=10
tent withmodelswithsignificantly
observed with Herschel, gas densities at 1000 AU an
5 mag. The initial abundances of CN, HCN and CS equal zero at dances ratio with fixed visual extinction AV = 5 mag and 107 yr
10 2 times
theaverageinterstellar
UV
field.
For
threedent signatures of UV fields were found (Kristensen e• observed
UVによって分子の存在量が変t = 0. The assumed cosmic-ray ionization rate is 1.3 ⇥ 1017 s 1 , after star formation began in the cloud.
withKarska
Herschel,gasdensitiesat
10008,AU
and
2017;
et
al.
2018).
Using
Figureweestimident signatures
UV fields
werefound (Kristensen
et adust to gas mass ratio is 0.01, dust grain radius is 10 5 cm andward Ser of
SMM1,
SMM3
and SMM4of 103 104 the2017;わっている。→UVのトレー
Karskaet discuss
al. 2018).
8, we themestimatgrain density is 3 g cm 3 .
value. We
theseUsing
valuesFigure
and compare
to
ward
Ser
SMM1,
SMM3
SMM4 of 103 104 the int
surements
Sectionand
5.3.
the CN/HCN column densities range from A.
0.7Mirocha
to 8.1 et(1al. 2021:= 2.3).
Signatures of UV
radiationaroundinlow-mass
protostars
value. We discussvalues and comparethem tooth
In ordertheseto understandthe chemistryleadinThus, the observed line ratios correspond to column densities
サーとして使用できる。
surements
in Section(e.g., Yıldız et al. 2015).
CN/HCN>
1 in5.3.
the presence of UV fields, both prod
Fig. irrespective
8: The columnofdensity
ratio
of CN to HCN from Nahoon
ratios of the order of ⇠1-12
the gasparameters.
each molecule
to be investigate
for a range of hydrogen densities and UV field strengths assum-In destruction
order to ofunderstandthe needchemistryleading⌫Wshows1 thedominant
reactionsat 50
K forboththreeproduc
UV fieing T =density
50 K. The
corresponding
range fromof ratiosfrom observaCN/HCN>in thepresenceof UV
fields,Fig. 8: The column
ratio
of CN to HCN
NahoonNu =(2)
3
1- weak10 ),needmedium
(G0 investigated.
= 10 1 101 ),0 = 10and radiativetransfer
arestrengths
shown in green(see Table
A
destructionof(Geachmolecule
to be
4.2. Chemical
for amodel
range oftionshydrogendensities
and models
UV field
assum1
6(G0 = 10 10 ). These reactions account for more th4). Yellow stars show the positions of Ser SMM1, SMM3,shows
and thedominanttotal
reactionsat 50 K for three UV
field
T = 50 K.SMM4
The corresponding
range
of ratios from at
observaIn order to calculate the total column density of a given The Nahooning
flux of all reactions, where
the reac
assuming
their gas theoreticalnumber densities
1000 AU from accumulated
31chemical
code
is
used
to
calculateabunweak(G
10 1 ), medium(Gmultiplied
101the), an
0 = 100 = 10
tions and radiativetransfermodels
are
shown
in
green
(see
Table
definedasreactants’abundancesbyremolecule, we use the following expression and adopt a gas tem- dances of molecules
Kristensen
et al. (2012).
1
for
a set
of physicalconditions
andUV field(G0 = 10106 ). Additional
These reactions
account
for
more
than
4).
Yellow
stars
show
the
positions
of
Ser
SMM1,
SMM3,
and
coefficient.
reactions,
where
CN
or
HCN
perature of 50 K (Yıldız et al. 2012).
2
strengths . It
is a well-known
almostchemicaltotal fluxof all reactions,
theinreactio
or destruction
is greaterthan 30%, whereare listed
Appen
SMM4
assuming theirgas purely
numbergas-phasedensities at1000 AU from accumulated
reactants’abundances
multiplied
code for astronomical(Wakelamrange
et al.
2015).
Eu Nu
Kristensen etapplications
al. run(2012).
e line) andthe regimeof strong UVfields (G0by> the
101 reac), thearefor a temperature
between
10 Theand 200 K and adefined
total as In
N
=
Q(T
)
exp(
)
,
(3)
3
6
tot
exc
coefficient.
Additional
whereorphotodisso
HCN proNahoon solver computeshydrogenthe chemical
in timedestruction
route reactions,of both HCN
and CNCN isdensitiesevolution
from 104 cm
to 10includcm 3 .
rochemical
kB T exc gu
or destruction
is greaterthan in30%,
are listed
in Appendi
UV photons.
Similarly,
mediumUV fields
CN is al• AV =UVがない場合にはHCNの存在量はCNよりも2-3桁多い。
Figure 7 showsmodel results
assuming
andtheselectedgas-grain
re- a visual extinc10 K,
Fig. 7: Contour plot of Nahoon sets of models of CN/HCN abun-ing 489 species and 7509 gas-phase1
destroyed
byofUV
photons,
andHCN
is>removedby dthtion of 5 magwhichcorresponds
to 200a lackofradiation. InIn the
where) refers
thefixed
temperature-dependent
partition
funcqual zeroat Q(T
regimestrongUVfields(G
10), theareon
runratefor acoefficients
temperature
range
between
10 Database
and
Kfor
andUV
a totalfrom
theKinetic0
dancesratiotowithvisual extinction AV =5 mag and107 yractions based
3 abundant3
with route
C+ , which
production
also CNrequires
UV radiatio
3 104iscm
that
case,
HCN
more
⇥ 10•17s 1for, after
destructionof bothHCN andis photodissocihydrogendensities
fromto 106 cm than
. CN by about 2-3 orderstion
the givenmolecule,
Eu isthe cloud.
upper energy level, gu is Astrochemistry(KIDA)
database.
starformation
began
in the<100
Kではガスの温度にはあまり依存しないため、
temperatureof 300corresponding
to theofof magnitude.
The resultscolumn assuming
density ratioof CN toHCN weakly
0 5 cmanddegeneracy, and kB is the Boltzmann constant. Appendix D
UV photons.
Similarly,
in K,
mediumUV fields
CNbulkis alsolevel
Figure in
7 shows
theismodela visual
extincThe UV radiation
Nahoondescribed
throughuntil
the&relationfrom low-mass protostars (Karska et al. 201
depends
on thegas temperature
100 K, so we fix thegas outflows
destroyedbyUV
photons,andHCN
isremoved
by
the
tion
of
5
mag
which
corresponds
to
a
lack
of
UV
radiation.
In
shows
the
columndensities
obtainedforallmolecules,
bothatbetween the visual extinction
AV andpact of photodissociation of HCN becomes dominant
T=50 Kで固定。
temperature
at 50theK. photodissociation ratewith C+ , which production also requires UV radiation.

compare the same emitting regions.

Class 0/I 天体の違い

UVFig.
radiationaround low-mass
11: Correlationsof protostars
line luminosity ratios with bolometric

e

,
-

a
,
n
n
e
x
r
e

(C ) form, which has a significant impact on chemical networks.
In starless, dark, non-turbulent clouds, HCN is more abundant than CN by about an order of magnitude (Pratap et al.
1997). This is in agreement with our model of a starless cloudafter 105 106 yr of cloud evolution (Figure 6). With the further•
CN/HCNのluminosity比と原始星の温度やluminosityの間に相関関
chemicalevolution of a starless cloud, the CN/HCN ratio decreases. In a weak UV field, the chemistry is similar to the star係はない。
less, dark,
non-turbulent interstellar cloud. Dominant formation
channels• of CN
and HCNare reactions of nitrogen with hydroClass
0/Iの間はCN/HCNの比は変化しない。
carbons (CH and CH2 , respectively), while destruction of CN ismostly dominated by the reactions with neutral oxygen or nitrogen. HCN is less reactive than CN, and reactions with neutral•
Herschel/PACSの観測でサンプル間に[OI]の強度に大きな差がな
atoms
are not very efficient in this case. Many reaction channels
driveいこととconsistentthe destruction of HCN,(Karska
but reactants
are less abundant
et al. 2018)。
than neutral atoms. The simultaneous impact of a few di↵erent
reactions is not as e↵ective as the reaction ruling the CN destruction. Those factors lead to the higher HCN abundances comparedto CN.
As the intensity of UV radiation increases, photodissociation and photoionization become more important. For strong radiation field, the destruction of CN is dominated by reaction:! C + N.
アウトフローのショックによるUV放射
temperature and luminosity of protostars. Class 0 protostars are CN
However, at intermediate UV field strength, photodissociation of
UV photons

marked with red dots, while Class I with black squares. The
Pearson coefficient of the correlation (r) is shown.

CN is not efficient and the reaction with neutral oxygen is important:
ショック前後
CN + O ! N + CO.
•
アウトフローのショック由来のUV放射による分子の存在量をモデル化
For intermediate and strong radiation fields, C+ is significantly
5.2. Chemical effects
more abundant than C. It opens a very e↵ective channel of HCN(Lehmann et al. 2020).
In the presence of strong UV radiation, HCN photodissociates destruction:
UV photons•
アウトフローのショックでUVが放射されるのは、HerschelのH2O
into CN and H, while CN requires even more energetic photons C! C+ + e –+(>12.4 eV) to be dissociated (van Dishoeck 1987). This should HCN + C! H + CNC+
(Wampfler et al. 2013;lead to a higher abundance of CN molecules and an increase CNC+とOHの存在量の観測結果から示唆されている+ e – ! CN + C
of the CN/HCN column density ratio. Despite many limitations The presenceof this channel leads to a significantly lower conKristensen et al. 2017)。
Article number, page 12 of 32

Post-shock•

観測結果のうち、CN/HCN比がもっとも高い領域に関しては、
Vsh=35 km/sのモデルとconsistent。
•

Fig. 13: The observed CN/HCN column density ratio comparedwith shock models with UV for a preshock density of 104 cm 3

モデルのよりも、 CN/HCN比が小さい傾向にある。