Candidate Water Vapor Lines to Locate the H$_{2}$O Snowline through High-Dispersion Spectroscopic Observations II. The Case of a Herbig Ae Star

2.1 MB·

by  Shota Notsu

Candidate Water Vapor Lines to Locate the H O Snowline
2
through High-Dispersion Spectroscopic Observations II. The Case
of a Herbig Ae Star
7
1
0 Shota Notsu1,8, Hideko Nomura2, Daiki Ishimoto1,2, Catherine Walsh3,4, Mitsuhiko Honda5,
2 Tomoya Hirota6, and T. J. Millar7

n 1Department of Astronomy, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho,
a
Sakyo-ku, Kyoto 606-8502, Japan
J
2Department of Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku,
6
Tokyo 152-8551, Japan
1
3Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

] 4School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK
P
5Department of Physics, School of Medicine, Kurume University, 67 Asahi-machi, Kurume, Fukuoka
E
830-0011, Japan
.
h 6National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
p
7Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, University
-
o Road, Belfast, BT7 1NN, UK
r 8Research Fellow of Japan Society for the Promotion of Science (DC1)
t
s
a [email protected]
[

This paper was received by The Astrophysical Journal (ApJ) on October 27th, 2016,
1
v and was accepted on January 13th, 2017.
1
8
3
4
0 ABSTRACT
.
1
Observationally measuring the location of the H O snowline is crucial for understanding the
0 2
planetesimal and planet formation processes, and the origin of water on Earth. In disks around
7
1 Herbig Ae stars (T∗ ∼10,000K,M∗ &2.5MJ), the position of the H2O snowline is further from
: the central star compared with that around cooler, and less massive T Tauri stars. Thus, the
v
i H2O emission line fluxes from the region within the H2O snowline are expected to be stronger.
X
Inthis paper,we calculatethe chemicalcompositionofaHerbig Ae disk usingchemicalkinetics.
r Next, we calculate the H O emission line profiles, and investigate the properties of candidate
a 2
water lines across a wide range of wavelengths (from mid-infrared to sub-millimeter) that can
locate the position of the H O snowline. Those line identified have small Einstein A coefficients
2
(∼10−6−10−3 s−1)andrelativelyhighupper stateenergies(∼ 1000K).Thetotalfluxestendto
increase with decreasing wavelengths. We investigate the possibility of future observations (e.g.,
ALMA, SPICA/SMI-HRS) to locate the position of the H O snowline. Since the fluxes of those
2
identified lines from Herbig Ae disks are stronger than those from T Tauri disks, the possibility
of a successful detection is expected to increase for a Herbig Ae disk.
Subject headings: astrochemistry— protoplanetary disks— ISM: molecules— sub-millimeter & infrared:
planetary systems— stars: formation
1
1. Introduction could be used to locate the position of the H O
2
snowline. This is because the water gas column
Observationally locating the position of the H O
2 density of the region inside the H O snowline is
2
snowline (Hayashi 1981; Hayashi et al. 1985) in a
high enough that all lines are optically thick as
protoplanetary disk is important. It will provide long as A > 10−6 s−1. On the other hand, the
ul
information on the physical and chemical con-
region outside the H O snowline has lower water
2
ditions in disks, such as the temperature struc-
gascolumndensitiesandlineswithlargerEinstein
ture, the dust-grain size distribution, and the wa-
Acoefficientshaveamoresignificantcontribution
ter vapor distribution in the disk midplane (e.g.,
to their fluxes since the lines are optically thin.
Oka et al. 2011; Piso et al. 2015), and will give
The wavelengthsof those candidate lines we iden-
constraints on the current formation theories of
tified to locate the position of the H O snowline
planetesimalsandplanets(e.g.,O¨berg et al.2011; 2
overlap with the capabilities of ALMA. In ad-
Okuzumi et al. 2012; Ros & Johansen 2013). It
dition, we calculated the profiles of lines which
will help clarify the origin of water on rocky
have been detected by previous spectroscopic ob-
planetsincludingthe Earth(e.g.,Morbidelli et al.
servations using Herschel (e.g., the ortho-H O
2
2000,2012,2016;Sato et al.2016). Banzatti et al.
63.32µmand538.29µmlines). Theselinesareless
(2015) and Cieza et al. (2016) recently showed
suited to locate the position of the H O snowline,
2
that the presence of the H O snowline leads to a
2 because they are not dominated in flux by the
sharpdiscontinuityintheradialprofileofthedust
region inside the snowline.
emission spectral index, due to the replenishment
of small grains through fragmentation because of
In this work (paper II), we extend our disk chem-
the change in fragmentation velocities across the
ical model and the H O line profile calculations
2
H O snowline. Through recent space and ground
2 to the case of a Herbig Ae disk. We discuss the
infrared spectroscopic observations for proto-
differences in disk chemical structures and line
planetary disks, some infrared H O lines, which
2 properties between the cases of a T Tauri disk
mainly trace the disk surface, have been detected
(paper I) and a Herbig Ae disk (this paper). We
(for more details, see e.g., Pontoppidan et al.
investigate the line properties in detail for can-
2010b; van Dishoeck et al. 2014; Blevins et al.
didate water lines to locate the position of the
2016; Banzatti et al. 2016; Notsu et al. 2016).
H O snowline over a wide wavelength range from
2
mid-infrared to sub-millimeter, and discuss the
The velocity profiles of emission lines from pro-
possibility of detecting such lines with future ob-
toplanetary disks are usually affected by Doppler
servations. The methods are outlined in Section
shiftduetoKeplerianrotationandthermalbroad-
2. The results and discussions are described in
ening. Therefore,thevelocityprofilesaresensitive
Sections3and4,respectively,andtheconclusions
to the radial distribution of the line-emitting re-
are listed in Section 5.
gions. Inourpreviouspaper(paperI,Notsu et al.
2016), we calculated the chemical composition
and the H2O line profiles in a T Tauri disk1, 2. Methods
and identified candidate H O lines especially at
2
sub-millimeter wavelengths, to locate the posi- The physical structures of the protoplanetary
tion of the H O snowline through future high- disk models used here are calculated using the
2
dispersion spectroscopic observations. Our calcu- methods in Nomura & Millar (2005) including X-
lations showed that the fluxes of H O lines with ray heating (Nomura et al. 2007). A more de-
2
small Einstein A coefficients (A ∼ 10−6 −10−3 tailed description of the background theory and
ul
s−1) and relatively high upper state energies computation of this physical model is described
(E ∼ 1000K) are dominated by the disk region in the original papers (Nomura & Millar 2005;
up
inside the H O snowline. Therefore, their profiles Nomura et al. 2007) and paper I (Notsu et al.
2
2016). Walsh et al. (2010, 2012, 2014a, 2015),
1Intheremainderofthispaper,wedefinetheprotoplanetary Heinzeller et al.(2011),Furuya et al.(2013),Notsu et al.
disksaroundTTauri/HerbigAestarsas“TTauri/Herbig (2015), and Notsu et al. (2016) used the same
Aedisks”.
physical models for a T Tauri disk and a Herbig
2
Fig. 1.— The total gas number density in cm−3 (top left), the gas temperature in Kelvin (top right), the
dust temperature in Kelvin (bottom left), and the UV flux in erg cm−2 s−1 (bottom right) of a Herbig Ae
disk as a function of the disk radius in au and height (scaled by the radius, z/r) up to maximum radius of
r =300 au.
3
Ae disk to study various chemical and physical z/r=0.1),becausethescaleheight2H oftheHer-
effects, and they also describe the calculation of bigAedisk(e.g.,H/r∼1.2atr =5au)issmaller
the physical structures in detail. than that for the disks around the T Tauri disk
(e.g.,H/r ∼1.7atr =5au). Thegasdensityand
In paper I (Notsu et al. 2016), we adopted the temperaturedistributionsofthedisksareobtained
physical model of a steady, axisymmetric Keple- self-consistently by iteratively solving the equa-
rian disk surrounding a T Tauri star with mass tions for hydrostatic equilibrium in the vertical
M∗=0.5MJ, radius R∗=2.0RJ, and effective directionandlocalthermalbalancebetweenheat-
temperature T∗=4000K (Kenyon & Hartmann ing and cooling of gas (Nomura & Millar 2005).
1995). In this paper, we adopt the physical The gas and dust temperatures throughout most
model of a disk surrounding a Herbig Ae star of the Herbig Ae disk, and the strength of the
with M∗=2.5MJ, R∗=2.0RJ, and T∗=10,000K UV flux in the disk surface of the Herbig Ae disk
(see also Walsh et al. 2015). In our disk physical are higher compared with those of the T Tauri
models, we adopt a viscous parameter α=10−2, disk, although the stellar UV radiation field in
a mass accretion rate M˙ =10−8M yr−1, and our Herbig Ae disk model has no excess emission
J
gas-to-dust mass ratio g/d = 100. The values components, apart from that in our T Tauri disk
of total disk mass are M ∼ 2.4 × 10−2M model. This is because the photospheric black-
disk J
for the T Tauri disk (Heinzeller et al. 2011), and body radiative flux from the central Herbig Ae
M ∼ 2.5×10−2M for the Herbig Ae disk. star is larger than that from the central T Tauri
disk J
We adopt the same compact and spherical dust- star. The strength of the X-ray flux in the disk
grain model of Nomura & Millar (2005). They surface of the Herbig Ae disk is lower compared
assume that dust and gas are well mixed, and with that of the T Tauri disk, since we adopted
that the dust grains consist of silicate grains,car- a smaller value of X-ray luminosity in the Herbig
bonaceous grains, and water ices. They adopt Ae disk (L ∼ 3×1029 erg s−1) compared with
X
the dust-grain size distribution which is consis- that in the T Tauri disk (L ∼1030 erg s−1).
X
tent with the extinction curve observed in dense To investigate the chemical structure of the
clouds (Mathis et al.1977; Weingartner & Draine Herbig Ae disk, we use a large chemical net-
2001). ThestellarUVradiationfieldinourHerbig work which includes gas-phase reactions and gas-
Ae diskmodelhasno excessemissioncomponents grain interactions (freeze-out of gas molecules
(e.g.,opticallythinhydrogenicbremsstrahlungra- on dust grains, and thermal and non-thermal
diationandLyman-αlineemission),althoughthat desorption from dust grains). The initial ele-
inourTTauridiskmodelhassuchexcessemission mental fractional abundances (relative to total
components(formoredetail,seeNomura & Millar hydrogen nuclei density) we use are the set of
2005,Walsh et al.2015andNotsu et al.2016). In atomic oxygen-rich low-metallicity abundances
Figure 1, we display the gas number density in from Graedel et al. (1982), listed in Table 8 of
cm−3 (top left), the gas temperature in K (top Woodall et al. (2007), which is the same set as
right, T ), the dust-grain temperature in K (bot- usedin paper I (Notsu et al.2016). We adoptthe
g
tom left, T ), and the wavelength-integrated UV same chemical network as described in paper I
d
fluxinergcm−2 s−1(bottomright)ofaHerbigAe (Notsu et al. 2016). Henning & Semenov (2013),
disk as a function of disk radius in au and height Dutrey et al. (2014), and Haworth et al. (2016)
(scaled by the radius, z/r). reviewed the recent development of calculations
for chemical structure in protoplanetary disks.
Herewefocusonthedifferencesbetweenthephys-
ical structures of the T Tauri disk (see Figure 1 Using the H O gas abundance distribution ob-
2
of paper I, Notsu et al. 2016) and the Herbig Ae tained from our chemical calculation described
disk. Thedensityintheatmosphereofthe Herbig in the previous paragraph, we calculate the H O
2
Ae disk (e.g., n = 6×1010 cm−3 at r = 5 au emission line profiles ranging from near-infrared
H
and z/r = 0.1) is lower than that of the T Tauri to sub-millimeter wavelengths from the Herbig
disk (e.g., n = 2×1011 cm−3 at r = 5 au and
H
2H = cs/Ω ∝ M∗−0.5Tg0.5, where cs and Ω are the sound
speedandKeplerianangularvelocity,respectively.
4
Ae disk assuming Keplerian rotation, and iden-
tify the lines which are the best candidates for
probing emission from the inner thermally des-
orbed water reservoir, i.e., within the H O snow-
2
line. We also study how the line fluxes and pro-
file shapes depend on the position of the H O
2
snowline. In paper I (Notsu et al. 2016), we
adopted the same calculation method to deter-
mine the H O emission line profiles from a T
2
Tauri disk (based on Rybicki & Lightman 1986,
Hogerheijde & van der Tak2000,Nomura & Millar
2005, and Scho¨ier et al. 2005), with the detailed
modelexplainedinSection2.3ofpaperI.Thecode
which we have built for calculating emission line
profiles is a modification of the original 1D code
called RATRAN3 (Hogerheijde & van der Tak
2000). Weadoptthedataoflineparametersinthe
LeidenAtomicandMolecularDatabaseLAMDA4
(Scho¨ier et al. 2005). Here we note that in our
method,weadopttheassumptionoflocalthermal
equilibrium (LTE) to obtain the level populations
of the water molecule (n and n ). In Section
u l
4.2, we discuss the validity of this assumption. In
addition, we set the ortho to para ratio (OPR) of
water to its high-temperature value of 3 through-
out the disk.
3. Results
3.1. The distributions of H O gas and ice
2
Figure 2 shows the fractional abundances (rela-
tive to total gas hydrogen nuclei density, n ) of
H
H Ogasand ice ina Herbig Ae disk as a function
2
of disk radius r and height scaled by the radius
(z/r). Here we focus on the differences in H O
2
distributions between the cases of a Herbig Ae
disk and a T Tauri disk (see Figure 2 of paper I, Fig. 2.—Thefractionalabundance(relativetoto-
Notsu et al. 2016). tal hydrogen nuclei density) distributions of H2O
gas (top) and H O ice (bottom) of a Herbig Ae
2
The H O snowline of the Herbig Ae disk ex- diskasafunctionofdiskradiusandheight(scaled
2
ists at a radius of r ∼ 14 au in the midplane by the radius, z/r) up to maximum radius of
(T ∼ T ∼ 120K), which is significantly larger r =300au.
g d
than that for the T Tauri disk model (r ∼ 1.6
au, see Figure 2 of paper I, Notsu et al. 2016).
This is because the gas and dust temperatures,
which are coupled in the midplane of the Herbig
3http://home.strw.leidenuniv.nl/~michiel/ratran/
4http://home.strw.leidenuniv.nl/~moldata/
5
Ae disk, are higher than that of our T Tauridisk.
InsidetheH Osnowline,thetemperatureexceeds Intheouterdisk,thefractionalabundanceofH O
2 2
the sublimation temperature under the pressure gas is also relatively high (∼ 10−8−10−7) in the
conditions in the midplane of the Herbig Ae disk hotsurfacelayerandattheH Osublimation(pho-
2
(T ∼ T ∼ 120K), and most of the H O is re- todesorption) front compared with the cold mid-
g d 2
leased into the gas-phase by thermal desorption. plane region of the outer disk (. 10−12−10−10),
Here we note that the sublimation temperature as also shown in the T Tauridisk model (paper I,
under the pressure conditions in the midplane of Notsu et al. 2016).
the Herbig Ae disk (T ∼ T ∼ 120K) is lower
g d
than that in the midplane of the T Tauri disk Here we note that the region with a high H O
2
(T ∼ T ∼ 150−160K, see paper I Notsu et al. gas abundance (∼ 10−4) in the disk midplane ex-
g d
2016). The region in the midplane of the Her- tends to a larger radius (r ∼10 au) at z/r & 0.1
big Ae disk where the temperature is around than at z/r ∼ 0 (r ∼ 7−8 au). This is not seen
100−200K is at a larger radius compared with in the T Tauri disk case (see Figure 2 of paper
that in the midplane of T Tauri disk, and the gas I, Notsu et al. 2016). This is because the scale
number density of such a region in the midplane height of the Herbig Ae disk (e.g., H/r ∼ 1.2 at
of the Herbig Ae disk is lower (n ∼ 1011−1012 r = 5 au) is smaller than that for the T Tauri
H
cm−3) versus (n ∼ 1012−1013 cm−3). Accord- disk (e.g., H/r ∼ 1.7 at r = 5 au) and the radi-
H
ing to Eq. (3)-(5) in Section 2.2.2 of paper I ation from the central Herbig Ae star is stronger
(Notsu et al. 2016), the sublimation temperature than that from the central T Tauri star, thus the
is higher if the gas number density is also higher. gas temperature of the Herbig Ae disk around
z/r ∼ 0.1 is higher. In contrast, for the T Tauri
The temperature of the region just inside the diskcase,sincethe diskscaleheightislargerthan
H O snowline in the Herbig Ae disk (between thatof HerbigAe disk,the valuesof gastempera-
2
7−8 au and 14 au) is T ∼ 120−170K; hence tureofthediskbetweenz/r∼0−0.1isconstant.
g
the gas-phase chemistry to form H O molecules
2
(e.g., O+H →OH+H and OH+H →H O+H) is ThetoppanelofFigure3showstheradialcolumn
2 2 2
not efficient compared with the inner region at a density profiles of H O gas and ice for both the
2
highertemperature(T >170K,r <7−8au). We T Tauridisk (see Figure 3 ofpaper I, Notsu et al.
g
pointoutthattheradialtemperatureprofileinthe 2016) and the Herbig Ae disk. In the Herbig Ae
midplane of the T Tauri disk is steeper than that disk case, the column density of H O gas and ice
2
in the midplane of the Herbig Ae disk, and this inthediskmidplaneflipsacrosstheH Osnowline
2
is another reason why the T Tauri disk does not as expected (r ∼ 14 au). The column density of
havesucharegionwitharelativelylargefractional H O gas is high (∼ 1020−1022 cm−2) in the in-
2
abundance of H O gas (∼10−8). A similar distri- ner high-temperature region of the disk midplane
2
butionofgas-phaseH OinthemidplaneofaHer- with r < 7−8 au, relatively high (∼ 1016−1019
2
bigAediskisreportedinFigure1ofWoitke et al. cm−2) in the midplane between 7−8 au and 14
(2009b). Here we also note that Eistrup et al. au, and in contrast, low outside the H O snow-
2
(2016) calculated the chemical evolution of a disk line (<1016 cm−2). The columndensity profile of
midplane under both molecularandatomic initial H O ice is roughly opposite. In the T Tauri disk
2
conditions as initial chemical abundances. They case, the column densities of H O gas and ice in
2
showed that in the latter atomic conditions, the the disk midplane flips across the H O snowline
2
abundance of H O gas and ice around the H O more steeply following the steeper temperature
2 2
snowline (∼10−6) is smaller than that for molec- gradient. The Bottom panel of Figure 3 shows
ular initial abundances (∼10−4). This is because the radial profiles of the column density in cm−2
O is formed in the gas-phasevia O+OH→O +H of H O ice and gas in the Herbig Ae disk, which
2 2 2
and remains in the gas phase since its sublima- have been vertically integrated from z =∞ to (i)
tiontemperatureis muchlowerthanthatofother −∞, (ii) z(τ = 1), (iii) z(τ = 1),
17.75µm 61.32µm
molecules like H O. This reactionroute competes and (iv) z(τ = 1). τ is the total optical
2 682.66µm λ
with gas-phase H O formation. depth value at each wavelength, λ, including gas
2
6
and dust components. In Section 4.3, we discuss
about this panel in detail.
Previous analytical models and numerical simula-
tions derived the position of the H O snowline of
2
1022 an optically thick disk for given parameters, such
−2m] 1020 as mass (M∗) and temperature (T∗) of the cen-
c tralstar,a viscous parameterα, anaccretionrate
sity [ 1018 M˙ , a gas-to-dust mass ratio g/d, and the average
en 1016 dust grain size a and opacity (e.g., Davis 2005;
D
n 1014 Garaud & Lin 2007; Min et al. 2011; Oka et al.
m
2011; Du & Bergin 2014; Harsono et al. 2015;
Colu 1012 HH22OO g icaes TT TTaauurrii Mulders et al. 2015; Piso et al. 2015; Sato et al.
1010 HH22OO g iaces HHeerrbbiigg AAee 2016),andsuggestedthatthe positionofthe H2O
1 10 100 snowline changes, as these parameters change. In
r [AU] the case of Herbig Ae disks with M∗ ∼ 2.5MJ,
M˙ ∼ 10−8M yr−1, g/d = 100, and a ∼ 0.1µm,
2] 1022 the position oJf the H2O snowline is ∼10−20 au.
−m 1020 In our calculations we use similar parameters for
y [c 1018 M∗, M˙ and a, and the H2O snowline appears at
sit a radius of around 14 au in the midplane, within
Den 1016 the range of previous studies.
n 1014
m
Colu 11001102 HHH2O22OO g ggaaas sstH H(tt62((2O168O712 g ...i736ca526esmmm mmmTToo)))===ttaa111ll 3.2. Hdi2sOk emission lines from a Herbig Ae
1 10 100
r [AU] InthisSection,wefirstdescribethedetailedprop-
ertiesofsevencharacteristicpurerotationalortho-
H O lines (see Table 1 and Section 3.2.1) for the
2
Herbig Ae disk. These seven lines (including the
ortho-H O682.66µmline)arecandidatesfortrac-
2
Fig. 3.— Top panel: The radial profiles of the
ing emission from the hot water reservoir within
vertically integrated column density in cm−2 of
the H O snowline. In Section 3.2.2, we describe
2
H O gas and ice in the T Tauri disk (green dotted
2 the properties of the 63.32 and 538.29µm lines,
line and black dashed dotted line) and the Her-
which are examples of lines which are less suited
big Ae disk (red solid line and blue dashed line).
to trace emission from the water reservoir within
Bottom panel: The radial profiles of the column
the H O snowline. We consider these two lines to
density in cm−2 of H O ice (blue dashed line) 2
2 test the validity of our model calculations, since
and gas in the Herbig Ae disk, which are verti-
the fluxes of these two lines from protoplanetary
cally integrated from z = ∞ to −∞ (red solid
disks have been observed with Herschel. The
line), to z(τ = 1) (black bold solid line),
17.75µm properties of near-, and mid-infrared H O emis-
2
to z(τ = 1) (green dotted line), and to
61.32µm sion lines which do not trace emission from the
z(τ =1)(orangedasheddottedline). Since
682.66µm hot water vapor within the H O snowline are also
τ at z =−∞ is lower than unity at r&10 2
682.66µm described in this subsection. Since we investi-
au, the radial profile of this case is plotted only
gated the profiles and properties of three lines
r .10 au.
(λ=682.66,63.32, 538.29µm)for the T Tauri disk
in paper I (Notsu et al. 2016), here we mainly fo-
cus on the differences between the line properties
betweenthe T Tauridisk and the Herbig Ae disk.
InSection 3.2.3andSection4.4,we showanddis-
7
cussothercandidatelineswhichtracetheemission in paper I (Notsu et al. 2016). In calculating all
fromthehotwatervaporwithintheH Osnowline lineprofilesinthispaper(seeFigures4,7,10,and
2
from mid-infrared to sub-millimeter wavelengths, 14),weassumethatthedistancedtotheobjectis
and their properties, especially the variation in 140pc(∼thedistanceofTaurusmolecularcloud),
line fluxes with wavelength. In Section 3.2.4, we and the inclination angle i of the disk is 30 degs.
show and discuss normalized radial cumulative
linefluxesforthe linesdiscussedinSections3.2.1- As shown in all panels in Figure 4, the contri-
3.2.3. butions from the optically thin surface layer of
the outer disk (r =14-30 au) are very small com-
In this paper, we show and discuss only the re- pared with those from the optically thick region
sults concerning ortho-H O lines, since the num- near the midplane of the inner disk (r <14 au),
2
berdensitiesandthefluxesofortho-H Olinesare and they show the characteristic double-peaked
2
larger than those of para-H O lines, due to the profile due to Keplerian rotation. This is because
2
assumption, OPR=3. The line selection process these lines, which have small Einstein A coeffi-
is described in detail in Section 3.2 of paper I cients (A ∼ 10−3 − 10−6 s−1) and relatively
ul
(Notsu et al. 2016). large upper state energies (E ∼1000K), mainly
up
tracethe hotH Ovaporinside the H O snowline.
2 2
In Section 2.3 and 3.2.1 of paper I (Notsu et al.
3.2.1. Candidate H2Oemission lines which trace 2016), we explained the reason why these lines
emission from the hot water vapor within have such properties.
the H O snowline
2
In the cases of candidate H O lines except the
Figure 4 shows the emission profiles of seven rep- 2
482.99µm and 682.66µm lines (see Figure 4), al-
resentative characteristic pure rotational ortho-
most all of the emission fluxes (> 95%) come
H O lines at λ=17.75µm(top left), 24.00µm (top
2
from the region with a high H O gas abundance
center), 61.32µm (top right), 94.17µm (middle 2
(∼10−4, r <8 au), and the position of the two
left), 482.99µm (middle center), 682.66µm (mid-
peaks and the rapid drop in flux density between
dleright),and933.28µm(bottom), forthe Herbig
the peaks contains information on the position
Ae disk. These lines have small values of A
ul
(∼ 10−3 − 10−6 s−1) and relatively large values of the outer edge of this region. In contrast, in
of upper E (∼ 700−1900K). They are repre- thecasesofthe482.99µmand682.66µmlines(see
up Figure4),mostoftheemissionfluxes(∼80−90%)
sentative candidate ortho-H O lines which trace
2
are emitted from the region with a high H O gas
emission from the hot water gas within the H O 2
2 abundance (∼10−4, r <8 au), and some fluxes
snowline. The H O 933.28µm, 682.66µm, and
2 (∼ 10−20%) are emitted from the region with a
482.99µm lines fall in ALMA band 7, 8, and 9,
relativelyhighH O gasabundance (∼10−8, r =8-
respectively. The H O 17.75µm line and 24.00µm 2
2
14 au). The position of the two peaks and the
line areQ bandlines atmid-infraredwavelengths,
rapid drop in flux density between the peaks con-
and the H O 17.75µm line falls in the wave-
2
tains information on the distribution of hot H O
length coverage of SPICA/SMI-HRS (see Section 2
gas within the H O snowline.
4.4). The detailed parameters,such as transitions 2
(J ), wavelength λ, frequency, A , E , crit-
KaKc ul up Figures 5 and 6 show the line-of-sight emissivity
ical density n = A /<σv >5, and total line
cr ul (emissivity times extinction, η e−τul; see Equa-
fluxes are listed in Table 1. In Table 1, we also ul
tion (14) of Paper I, Notsu et al. 2016) and the
show the values of the total fluxes from both the
total optical depth, τ (gas emission and dust)
Herbig Ae disk and the T Tauri disk (see also pa- ul
distributions of these seven H O lines, respec-
perI,Notsu et al.2016). Incalculatingthevalues 2
tively. We assume that the inclination angle, i, of
fromtheTTauridisk,weusethesamemethodas
the disk is 0 deg in making these figures (see Fig-
ures 5, 6, 8, 9, and 13), and thus the line-of-sight
5<σv>isthecollisionalratesfortheexcitationofH2Oby direction is from z = +∞ to −∞ at each disk
H2 andelectronsforanadoptedcollisionaltemperatureof
200KfromFaure&Josselin(2008). radius. In the left panels of Figure 5, we over-
8
Fig. 4.— The velocity profiles of seven characteristic pure rotational ortho-H O lines at λ=17.75µm (top
2
left),24.00µm(topcenter),61.32µm(topright),94.17µm(middleleft),482.99µm(middlecenter),682.66µm
(middleright),and933.28µm(bottom),whichhavesmallA andlargeE ,fromtheHerbigAedisk. These
ul up
arecandidateH OlinestotracethehotwatervaporwithintheH Osnowline. Incalculatingthelineprofiles
2 2
in this paper (see Figures 4, 7, 10, and 14), we assume that the distance to the object d is 140pc (∼ the
distance of Taurus molecular cloud), and the inclination angle of the disk, i, is 30 degree. The parameters
andtotalfluxesofthese H O linesarelistedinTable1andB.1. Red solid lines arethe emissionline profiles
2
frominside8au(=theinnerhightemperatureregion),blue dashed linesarethosefrominside14au(∼inside
theH Osnowline),green dottedlinesarethosefrom14-30au(∼outsidetheH Osnowline),andblack dashed
2 2
dotted lines are those from the total area inside 30 au.
9
Table 1: Calculated representative ortho-H O line parameters and total line fluxes
2
J λ1 Freq. A E n HAe flux2,3 TT flux3,4
KaKc ul up cr
[µm] [GHz] [s−1] [K] [cm−3] [W m−2] [W m−2]
6 -5 17.754 16885.840 2.909×10−3 1278.5 8.3×1010 4.1×10−17 2.3×10−20
52 05
5 -5 23.996 12493.205 2.696×10−4 1067.7 1.9×109 9.4×10−18 6.4×10−21
50 05
5 -6 61.316 4889.280 2.686×10−4 878.1 4.1×108 5.9×10−18 3.5×10−20
41 16
6 -7 94.172 3183.464 3.387×10−4 1278.5 3.1×108 1.8×10−18 1.6×10−20
52 25
5 -4 482.990 620.701 1.106×10−4 732.1 3.3×106 5.3×10−20 1.1×10−21
32 41
6 -5 682.664 439.151 2.816×10−5 1088.7 1.0×106 1.4×10−20 3.1×10−22
43 50
10 -9 933.277 321.226 6.165×10−6 1861.2 4.7×106 2.3×10−21 7.8×10−23
29 36
8 -7 63.324 4734.296 1.772 1070.6 1.5×1010 1.1×10−16 5.7×10−18
18 07
1 -1 538.289 556.936 3.497×10−3 61.0 2.9×107 7.2×10−20 1.1×10−20
10 01
17 -16 12.396 24184.126 7.728 5780.8 1.1×1011 6.7×10−17 5.3×10−19
413 314
13 -12 12.453 24073.032 1.053 4212.6 1.1×1013 6.9×10−17 2.5×10−19
76 49
7 -6 4.958 60463.186 3.260 4180.4 1.6×1013 2.2×10−16 1.1×10−18
61 52
7 -6 4.432 67646.817 2.080×10−4 4180.4 6.5×1011 5.0×10−20 8.1×10−23
61 34
1Incalculatingthevalueoflinewavelengthfromthevalueoflinefrequency,weusethevalue
ofspeedoflightc=2.99792458×108 ms−1.
2 ThetotalfluxofeachemissionlinefromtheHerbigAedisk.
3 In calculating the total fluxes of these H2O lines, we use a distance of d=140pc and an
inclinationangleofi=30degree.
4 The total flux of each emissionline from the T Tauri disk (see also paper I, Notsuetal.
2016).
10