Kinematic Distance of Galactic Planetary Nebulae

Kinematic Distances of Galactic Planetary Nebulae

A. Y. Yang1 1 , W. W. Tian1 1 1 , H. Zhu1 1 , D. A. Leahy1 , D. Wu1 1 1 Key Laboratory of Optical Astronomy, National Astronomical Observatories,
Chinese Academy of Sciences, Beijing 100012, China
University of Chinese Academy of Science, 19A Yuquan Road, Beijing 100049, China
Department of Physics Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Canada
College of Information Science and Technology, Beijing Normal University, Beijing 100875, China
Beijing Key Laboratory of Digital Preservation and Virtual Reality for Cultural Heritage, Beijing 100875, China
Email: tww@bao.ac.cn
1affiliationmark:
Abstract

We construct H i absorption spectra for 18 planetary nebulae (PNe) and their background sources using the data from the International Galactic Plane Survey. We estimate the kinematic distances of these PNe, among which 15 objects’ kinematic distances are obtained for the first time. The distance uncertainties of 13 PNe range from 10 to 50, which is a significant improvement with uncertainties of a factor two or three smaller than most of previous distance measurements. We confirm that PN G030.200.1 is not a PN because of its large distance found here.

Subject headings:
(ISM:) planetary nebulae: general—ISM: kinematics and dynamics—ISM: clouds—stars: distances

1. Introduction

Distances, as a basic physical parameter of planetary nebulae (PNe), are crucial to study their size, luminosity, ionized mass, formation rate, space density and Galactic distribution. However, distances are still not well determined for the majority of total 3500 PNe (Kwitter et al., 2014). For an individual PN, different methods may lead to different distances. So far, there are only about thirty PNe having their distance measurements with uncertainties less than .

Nine popular methods have been used to measure the distances of PNe, including trigonometric parallax (e.g., Harris et al., 2007), cluster member (e.g., Jacoby et al., 1997), expansion parallax (e.g., Terzian, 1997), spectroscopic parallax (e.g., Ciardullo et al., 1999), reddening (e.g., Gathier et al., 1986b), Na D absorption (e.g., Napiwotzki & Schoenberner, 1995), determinations of central star gravities (e.g., Mendez et al., 1988), statistical method (revised Shklovsky method, e.g., Shklovskii, 1956) and kinematics method (e.g., Gathier et al., 1986a).

Hydrogen is the most abundant element in the universe and H i atom clouds are broadly distributed in the Milky Way (Dickey & Lockman, 1990). The 21 cm H i absorption line has been widely used to measure kinematic distances of H i clouds and radio strong sources associated. When a H i cloud is located in front of or behind a strong radio source, we are usually able to detect a H i absorption feature or only an emission line from the cloud. The velocity of the emission/absorption feature can be converted into a distance based on the axisymmetric rotation curve model for the Galaxy. The distance or distance limit of the source can be estimated from the distance of the H i cloud. However, this method faces two main challenges. One is the kinematic distance ambiguity (KDA) for sources located inside the solar circle, as each radial velocity along given line of sight corresponds to two distances equally spaced on either side of the tangent point. The KDA usually can be solved by integrated consideration of H i absorption/self-absorption, CO emission and H i absorption of background sources. Another challenge is to construct a reliable H i absorption spectrum to a radio source due to the uneven H i background in the Galaxy. In order to minimize the second effect, Tian et al. (2007) and Leahy & Tian (2008) developed revised methods to construct H i absorption spectra. The methods have been applied to several types of Galactic objects successfully, e.g., PNe (Zhu et al., 2013), supernova remnants and H ii regions (e.g., Leahy & Tian, 2008; Tian & Leahy, 2008).

In this paper, we systematically construct the H i absorption spectra of PNe which are located in the sky region of the International Galactic Plane Survey (IGPS).  H i absorption features in the spectra are used to determine the PNe’s distances. This paper is organized as follows: the data and the revised methods are introduced in Section 2. In Section 3, we apply the methods to estimate individual PN distance. Summary is given in Section 4.

2. Data Analysis

2.1. Data

PN G           Survey Ref. Background Sources
Name          mJy
G020.901.1 20.999 -1.125      249.07.5 V CK98 21.345  0.630
21.500  0.885
G029.000.4 29.079 0.454      159.015 V CK98 28.800   0.175
28.825   0.230
29.098   0.545
G030.200.1 30.234 -0.139       V A11 29.930   0.055
30.535   0.020
30.685   0.260
29.960   0.020
G051.500.2 51.509 0.167      84.0 V LCY05 51.775   0.800
50.625   0.030
50.950   0.850
G052.101.0 52.099 1.043      455.113.7 V IPHAS09 52.235   0.745
52.750   0.335
G055.500.5 55.507 -0.558      84.12.6 V CK98 55.525   1.150
55.995   1.195
55.775   0.250
G069.700.0 69.800 0.004      87.12.6 V CK98 68.755   0.275
70.155   0.090
G070.701.2 70.674 1.192      949.633.4 C IPHAS09 71.225   1.445
70.690   0.630
70.600   1.380
G084.903.4 84.930 -3.496      137341 C CK98 85.120   3.100
84.445   2.915
G089.000.3 89.002 0.376      260.57.8 C IPHAS09 88.825   0.925
88.465   0.004
89.650   0.925
G107.802.3 107.845 2.314      58122.8 C IPHAS09 108.755   2.575
G138.802.8 38.816 2.805      153.1 5.8 C CK98 138.795   2.140
G147.402.3 147.401 -2.307      77.8 2.4 C IPHAS09 146.625   2.690
147.950   2.645
G169.700.1 169.653 -0.077      135.35.1 C IPHAS09 169.080   0.245
170.330   0.225
G259.100.9 259.149 0.940      34512 S CK98 257.902   0.844
257.913   0.655
G333.900.6 333.930 0.686      294.89.7 S BPF11 333.723   0.377
332.967   0.777
G352.600.1 352.675 0.144      37838 S CK98 352.588   0.167
351.616   0.177
353.408   0.355
G352.800.2 352.828 -0.259      47447 S CK98 352.588   0.167
352.854   0.189
353.408   0.355

Note. – The first three columns give the name and Galactic coordinates. Column (4) gives the flux density at 1.4 GHz. The survey names and references are given in the next two columns. The final two columns give the Galactic coordinates of background sources. References related in table are as follow: IPHAS09-Viironen et al. (2009), CK98-Condon & Kaplan (1998), LCY05-Luo et al. (2005), BPF11-Bojičić et al. (2011), A11-Anderson et al. (2011). a–the flux at 8.7 GHz is 752mJy for PN G030.200.1.

Table 1Information of PNe and background sources

The 1420 MHz radio continuum and H i-line emission data come from IGPS (the Very Large Array Galactic Plane Survey (VGPS)(Stil et al., 2006), the Southern Galactic Plane Survey (SGPS) (McClure-Griffiths et al., 2005), and the Canadian Galactic Plane Survey (CGPS) (Taylor et al., 2003)). The project surveys the Galactic disk from longitudes 18 to 67, 255 to 357 and 65 to 175, respectively. For CGPS, the continuum image at 1420MHz has a spacial resolution of 1 and H i spectra line images have a resolution of 1 1 1.56 km . At declination , the synthesized beam is 49 49 for 1420 MHz and 58 58 1.32 km for H i in the survey of CGPS. SGPS has a resolution 100 for continuum and 2 2 1 km for H i data. The   spectral line data from the Galactic Ring Survey of the Five College Radio Astronomical Observatory (FCRAO) 14 m telescope (Jackson et al., 2006) has an angular and spectral resolution of 46 and 0.21 km at longitudes from 18 to 52 and latitudes between 1 and 1. The   (J=10) spectral line data from the FCRAO CO Survey of the Outer Galaxy has an angular and spectral resolution of 45 and 0.98 km between Galactic longitudes 102.49 — 141.54 and latitudes 3.03 — 5.41 (Heyer & Terebey, 1998).

In this work, we construct the H i absorption spectra of the PNe with flux density larger than 50 mJy at 1420 MHz in the IGPS. By checking their H i spectra one by one visually, 18 of them show reliable absorption features. We analyze the 18 PNe in this paper. For each PN, at least one bright nearby background source has been chosen as a comparison with the PN in order to understand the PN’s H i  absorption spectrum. The parameters of 18 PNe and their background sources are shown in Table 1.

2.2. To obtain a reliable H i absorption spectrum

Based on the knowledge of radiation transfer, the brightness temperature of source () and background () that have continuum emission subtracted can be determined by the equations:

(1)
(2)

So, we can obtain the absorption spectrum of H i,

(3)

Where, is the spin temperature of H i cloud, and are the continuum brightness temperatures of source and background. The H i absorption spectrum is usually represented by or sometimes by .

To construct a H i absorption spectrum, traditionally one usually chooses the source and background regions separately. This could increase the possibility of false absorption spectrum caused by the different distributions of H i clouds along the two lines of sight. Nevertheless, Tian et al. (2007) and Leahy & Tian (2008) proposed revised methods by selecting the background region directly surrounding the source region to minimize the possibility of a false H i absorption spectrum. In addition, they extracted CO emission spectrum in the source direction and constructed H i absorption spectra of nearby strong background sources with their angular separation not exceeding 1 from target source to understand the target source’s absorption spectrum better. What’s more, when it is possible, H i self absorption resulting from cold H i cloud absorbing emission from background warm H i cloud at the same velocity has been used to reduce the KDA problem in the methods (e.g., Leahy & Tian, 2010; Tian et al., 2010).

3. Kinematic Distance Measurement to Planetary Nebulae

3.1. The model

Figure 1.— The relation between heliocentric distance and radial velocity in the four quadrants in the direction (, ) in Galactic coordinates, using a Galactic circular rotation curve model and adopting a galactocentric distance of =7.62 kpc and a rotation velocity of =220  km s.

The methods of determining distances are based on the flat Galactic circular rotation curve model. For a given PN at a distance from the Sun in the direction of (, ) in Galactic coordinates, the relation between the heliocentric distance and the galactocentric distance can be written as

(4)

where =7.620.32 kpc (Eisenhauer et al., 2005), the distance to the Galactic center from the Sun. However, is still uncertain (e.g. Bovy et al., 2012). Assuming circular orbits, the rotation velocity at galactocentric distance is given by

(5)

where is the radial velocity corresponding to the Local Standard of Rest (LSR), and =220  km s is the IAU adopted velocity at the LSR. In this work, we focus on the relation between the heliocentric distance and the radial velocity . Since can be expressed by

(6)

where R is related to in equation (5), the heliocentric distance can be written as a function of the radial velocity , which has different forms of expression in the four quadrants of the Galactic coordinates, see Fig. 1. In general, we analyze the spectra of PNe and their background sources to determine the kinematic distances of PNe assuming . In some special cases, when the maximum observed radial velocity (tangent point velocity) in the PN spectrum is much larger than the expected value, i.e., , we consider linearly increasing from =220 km s to as R reduces to the value at the tangent point. The same situation has been discussed in Leahy et al. (2008). We note that Reid et al. (2007) had updated the value with =224 km s and =242 km s. Reid et al. (2009) also found a higher rotation velocity of =25416 km s by measuring the trigonometric parallaxes and proper motions of masers with the Very Long Baseline Array data. Likewise, Leahy et al. (2008) and Levine et al. (2008) suggested a higher rotation velocity at longitude near 53.

3.2. Application to Planetary Nebula

We estimate distances of 18 PNe by taking 3 as the minimum level of significance for the detection of a H i absorption feature, where is the standard deviation calculated from the no emission baseline of PN H i spectrum. The distance uncertainty includes that caused by an average random velocity of H i  clouds, i.e., 6 km s (Crovisier, 1978; Shaver et al., 1982; Anantharamaiah et al., 1984). For each PN, at least one bright background source within an angular separation of 1 from the PNe has been chosen. The spectra are used to compare with the PN’s in order to understand the PN’s absorption spectrum. The 1420 MHz continuum images of both PNe and background sources are displayed in Fig. 2 to Fig. 19, together with their H i absorption spectra. The distance for each individual PN is discussed below, taking =7.62 kpc.

PN G020.901.1 (Fig. 2):

Fig. 2 shows the 1420 MHz continuum image and H i spectra of PN G020.901.1 and its nearby background sources (G021.30.63, G021.50.89). The PN is fainter in radio than both G021.30.63 and G021.50.89 so that the PN H i absorption spectrum shows more noise than the others. Absence of absorption at the tangent point velocity (100 km s) for both PN G020.901.1 and G021.50.89 implies they are likely located in front of the tangent point (7.10.6 kpc). The spectrum of G021.30.63 shows absorption features at 105 km s and negative velocities, which supports that this source is further than both PN G020.901.1 and G021.50.89. The absorption feature at 62 km s is probably not real since the absorption is very close to 3. The reliable absorption feature at 45 km s (e=0.44) indicates a lower limit distance of 3.10.3 kpc for the PN, i.e., the nearside distance for this velocity.

For PN G020.901.1, Cazetta & Maciel (2001) found a distance of 2.4 kpc based on the relation between distance and the surface gravity of central star of PN (  ). This kinematic distance of 3.10.3 kpc is reasonably consistent with the surface gravity distance, and larger than previous statistical distances of 1.75 kpc by Cahn et al. (1992), 1.66 kpc by van de Steene & Zijlstra (1995), 1.74 kpc by Zhang (1995), 2.29 kpc by Stanghellini et al. (2008) and 1.59 kpc by Phillips (2004).

PN G029.000.4 (Fig. 3):

Although the background sources near PN G029.000.4 show clear absorption spectra, the PN spectrum is complex. The prominent emission at the tangent point (100 km s) and the absence of an absorption feature at the velocity in the PN spectrum indicate an upper limit distance of 6.61.0 kpc for the PN. One probable absorption feature at 60 km s implies a lower limit distance of 3.50.3 kpc.

For this PN, a distance of 1.2 kpc has been derived by Maciel (1984) assuming a relationship between the nebular ionized mass and radius, which is smaller than our result.

PN G030.200.1 (Fig. 4):

PN G030.200.1 is a PN candidate suggested by Anderson et al. (2011). The absorption features of the PN candidate and four H ii regions appear up to the tangent point velocity (110 km s), which indicates all five objects are beyond the tangent point, i.e., 6.60.9 kpc. The absence of absorption at negative velocity in the PN spectrum implies the PN is inside the solar circle (13.20.5 kpc). The obvious absorption feature in the PN spectrum and absence of absorption in spectra of all background sources at 40 km s imply that the PN is likely beyond the far-side distance of 40 km s, i.e., 10.70.3 kpc. Based on these information, the PN sits between 10.70.3 kpc and 13.20.5 kpc.

PN G051.500.2 (Fig. 5):

Based on the Galactic circular rotation curve model and the IAU adopted parameters of =220 km s, the tangent velocity is expected to be 48 km . This is much smaller than the observed value of  km s obtained from the H i emission spectrum in Fig. 5. This higher could be due to spiral arm velocity perturbation near the tangent point in the direction of =51.5 (Dobbs et al., 2006). If  km s, the rotation velocity would be as high as 242 km s. In fact, Levine et al. (2008) found a high rotation velocity of 236 km s at longitude near 53. In addition, the high rotation velocity is also obtained in the H i spectra of PN G052.101.0 and PN G055.500.5. Altogether, we calculate the kinematic distance to the PN using =7.62 kpc, =220 km s and =243 km s.

The PN spectrum reveals absorptions appear up to the tangent point velocity, giving a lower limit distance of 4.71.4 kpc. The absence of any absorption feature at negative velocities in the PN spectrum means that the PN is within the solar circle, giving an upper limit distance of 9.50.4 kpc.

PN G052.101.0 (Fig. 6):

Similar to PN G051.500.2 , the observed tangent point velocity of 68 km s from the PN H i spectrum is larger than the expected value of 46 km s when taking commonly used parameters of =220 km s. This leads to a rotation velocity up to =242 km s. Fig. 6 shows absorption features in the spectra of the PN and two H ii regions (G052.20.75, G052.70.3) up to the tangent point velocity (68 km ), revealing all three objects are beyond the tangent point. So the lower limit distance for this PN is 4.71.4 kpc. Bright H i emission is detected at 48 km in the three spectra, whereas the absorption feature at this velocity is detected only in the spectra of two H ii regions. This implies that the PN is in front of H i at its far-side distance of 5.60.8 kpc.

PN G055.500.5 (Fig. 7):

The observed tangent point velocity (55 km s ) in the PN spectrum is larger than the expected value (38 km s ), which suggests that the rotation velocity is = 236 km s at the tangent point. Absorption features at the tangent point velocity in the spectra of the PN as well as three background sources  (G055.501.1, G055.901.2 and G055.700.2 ) indicate that all four objects are beyond the tangent point. Therefore, the lower limit distance is 4.31.5 kpc for the PN. Absence of absorption in the PN spectrum at negative velocity implies that the PN is within the solar cycle. So we suggest that the distance of the PN is between 4.31.5 kpc and 8.60.4 kpc.

Giammanco et al. (2011) suggested a distance of 2.90.4 based on distance-extinction relationship in the direction toward the PN. Zhang (1995) derived a distance of 3.17 kpc by using the relation between the radio continuum surface brightness and the nebular radius. Stanghellini et al. (2008) obtained a distance of 3.68 kpc by the revised relation of ionized mass and optical thickness. So our lower limit distance of 4.31.5 kpc for the PN G055.500.5 is reasonable.

PN G069.700.0 (Fig. 8):

The PN spectrum has low S/N due to its low brightness. Significant absorption features are detected at the tangent point velocity and at negative velocities in the spectra of both the PN and its background sources, hinting that they are all beyond the solar circle (= 5.30.7 kpc). According to the noise level (3 =0.23), the H i emission and absorption features at 64 km s reveal a lower limit distance of 11.10.6 kpc for the PN. The presence of H i  emission at -73 km s and the absence of an absorption feature at the same velocity indicate an upper limit distance of 12.00.7 kpc. In summary, PN G069.700.0 has distance between 11.10.6 kpc and 12.00.7 kpc, which is much larger than previous distances, e.g., 3.31 kpc by (Cahn et al., 1992), 3.26 kpc by Zhang (1995), 4.23 kpc by Stanghellini et al. (2008), 3.09 kpc by van de Steene & Zijlstra (1995) and 2.96 kpc by Phillips (2004). So we prefer to keep an open question for its distance.

PN G070.701.2 (Fig. 9):

Based on the observed tangent point velocity of 22 km s in the PN spectrum, we take a rotational velocity =230 km s at the tangent point in the direction =70.7. The fact that the H i absorption features of the PN and three background sources appear at the tangent point velocity implies all sources are beyond the tangent point. So we obtain a lower limit distance of 2.51.6 kpc for the PN . There are clear absorption features at negative velocities in nearby sources spectra, while no absorption feature is detected at these velocities in the PN spectrum. This implies the PN is within solar circle (5.00.7 kpc). So PN G070.701.2 is between 2.51.6 kpc and 5.00.7 kpc.

Bally et al. (1989) have given a distance of 4.51.0 kpc using the line width of CO emission and angular radius of CO cloud. Therefore, the upper distance of 5.00.7 kpc is suitable for the PN.

PN G084.903.4 (Fig. 10):

Fig. 10 shows the tangent point velocity (18 km s) towards the PN, which is larger than the expected value (0.8 km s). We obtain the rotation velocity =237 km s at the tangent point in the direction =84.9. The H i spectra of the PN and two background sources show clear H i  absorption features from 0 km s up to the tangent point (18 km s), hinting the PN and two background sources are beyond the tangent point. So we obtain the lower limit distance of 0.7 kpc for this PN. The prominent H i emission at 20 km s appears in the spectra of the PN as well as two nearby background sources, whereas its respective absorption feature is detected only in two background sources. This gives an upper limit distance of 4.30.6 kpc for the PN. Hence, the distance of the PN is between 0.7 kpc and 4.30.6 kpc.

This PN, named NGC 7027 as the most luminous Galactic PN, has a distance measured by various methods, such as statistical distances (0.7 kpc, Maciel (1984); 0.63 kpc, van de Steene & Zijlstra (1995); 0.64 kpc, Zhang (1995)), reddening (1.15 kpc, Navarro et al., 2012), expansion parallax (0.7030.095 kpc, Hajian et al. (1993); 0.981.0 kpc, Zijlstra et al. (2008); 0.880.15 kpc, Masson (1989); 0.680.17 kpc, Mellema (2004)). In fact, Pottasch et al. (1982) gave a upper limit distance 4.5 kpc also measured by comparing the H i absorption feature at 20 km s between the PN and a background source. So the lower limit distance 0.7 kpc is reliable for PN G084.903.4.

PN G089.000.3 (Fig. 11):

The disagreement between the observed tangent point velocity (10 km s) shown in Fig. 11 and the expected value (0.03 km ) may be due to random motions of H i clouds at the tangent point in the direction =89. Fig. 11 shows H i spectra of the PN and background sources. The absorption features at 70 km s and 40 km s are likely not real, and two significant absorption features at 20 km s and 0 km s indicate that a reliable lower limit distance for this PN is 3.50.6 kpc. No reliable upper limit distance can be determined for this PN.

The distance of this PN (also named NGC 7026) has been investigated previously by using H i absorption (2.51.0 kpc, Gathier et al., 1986a), statistical method (e.g., 2.35 kpc, Stanghellini et al. (2008); 2.03 kpc, Zhang (1995)), reddening (e.g., 1.570.65 kpc, Kaler & Lutz (1985); 2.3 kpc, Pottasch (1983)), surface gravity method (e.g., 3.5 kpc, Zhang (1993); 4.2 kpc, Cazetta & Maciel (2000)), spectroscopic method (1.9 kpc, Gruendl et al., 2004). Our result is reasonably consistent with surface gravity distance and larger than others. Actually, Gathier et al. (1986a) found a weak absorption at 20 km s in the PN spectrum, but they did not take this absorption as clear evidence to constrain its distance. The 7 km s absorption feature they chose for the lower limit distance of 2.51.0 kpc is also detected in our data. Since our data has higher resolution and more sensitive than before, the absorption at 20 km s detected in our work can be used to determine a more reliable lower limit distance of 3.50.6 kpc for this PN.

PN G107.802.3 (Fig. 12):

The absorption features at positive velocity in both the PN and G108.702.57 are partly due to a cloud with anomalous motion. Clear absorption features are present at 30 km s, 60 km s and 105 km s in the spectrum of background source G108.702.57, while no absorption features are detected at the velocities in the PN spectrum. This implies the PN is in front of the H i cloud at 30 km s, i.e, 2.80.5 kpc. The CO emission, H i emission and absorption features at 12 km s in the PN spectrum indicate a lower limit distance of 1.20.6 kpc. Therefore, the distance of PN G107.802.3 is between 1.20.6 kpc and 2.80.5 kpc.

For this PN, also named NGC 7354, the distance has been measured by various methods. Gathier et al. (1986a) suggested a H i absorption distance 1.50.5 determined by the nearby H ii regions of the PN. Giammanco et al. (2011) obtained a distance of 1.00.15 kpc based on the distance-extinction relationship in the direction toward the PN. Zhang (1993) gave a distance of 2.1 kpc by the surface gravity method. The revised Shklovshy method suggested distances of 1.27 kpc by Cahn et al. (1992), 1.3 kpc by Zhang (1995), 1.23 kpc by van de Steene & Zijlstra (1995), 1.19 kpc by Phillips (2004), and 1.70 kpc by Stanghellini et al. (2008). So the lower distance of 1.20.6 kpc seems reasonable for the PN.

PN G138.802.8 (Fig. 13):

There are clear H i absorption and CO emission features at 42 km s in the direction of G138.802.14, while similar absorption is not detected in the PN spectrum. This indicates that the PN is in front of the H i cloud at42 km s. The PN spectrum reveals one reliable H i absorption feature at 20 km s. Therefore, we obtain a lower limit distance of 1.60.5 kpc and an upper limit distance of 3.80.8 kpc.

PN G138.802.8 (also named IC 289) has statistical distances of 1.43 kpc by Cahn et al. (1992), 1.68 kpc by Zhang (1995)), 1.45 kpc by Stanghellini et al. (2008), 1.18 kpc by Phillips (2004), and 1.48 kpc by van de Steene & Zijlstra (1995); as well as a reddening distance of 2.710.195 kpc (Kaler & Lutz, 1985). So we suggest a distance of 1.60.5 kpc for the PN.

PN G147.402.3 (Fig. 14):

Both H i emission and absorption features at 35 km s appear in the spectra of the PN as well as its nearby background sources. This implies that the PN is behind the H i cloud at 3.60.9 kpc. In addition, the presence of clear H i emission and the absence of absorption at 60 km s in the PN spectrum indicates that the PN is in front of the H i cloud at 8.71.7 kpc. Overall, the distance of the PN is between 3.60.9 kpc and 8.71.7 kpc.

The distance of the PN was measured by several methods previously, i.e., surface gravity distance of 2.23.1 kpc by Cazetta & Maciel (2001), the revised Shklovsky distances of 3.39 kpc by Phillips (2004) and 3.53 kpc by Zhang (1995), as well as a reddening distance of 3.30.35 kpc by Giammanco et al. (2011). These are consistent with our lower limit distance 3.60.9 kpc.

PN G169.700.1 (Fig. 15): This PN is most likely a H ii region as suggested by Zijlstra et al. (1990), which is close to the Galactic plane (see Fig. 15). The H i emission and absorption features at 32 km s in spectra of the PN and the background sources imply they are beyond the H i cloud at 14.7 kpc, see Fig. 1 (upper-right panel). This lower limit distance is derived by considering the average random velocity 6 km s of H i clouds. No upper limit distance can be derived. Our lower limit is much larger than previous measurements, i.e., 1.37 kpc by Cahn et al. (1992), 1.86 kpc by Zhang (1995), 1.26 kpc by Phillips (2004), 1.39 kpc by Stanghellini et al. (2008). So we prefer to keep an open question for its distance.

PN G259.100.9 (Fig. 16):

There is strong continuous H i emission and absorption between 0 to 12 km s in the PN spectrum (Fig. 16), but no absorption features appear up to the tangent point velocity after 12 km s (3=0.27). This means that the PN is beyond the near side for 12 km s, i.e., 1.60.6 kpc. Unlike the PN spectrum, the two background sources show absorption features at velocities of 20 km s and 40 km s. This implies that the PN is in front of the H i at 20 km s,i.e., 2.40.6 kpc. So the distance of the PN is between 1.60.6 kpc and 2.40.6 kpc. In comparison with previous work obtained by statistical method (0.9 kpc, Cahn et al. (1992); 1.07 kpc, Zhang (1995)) and Spectroscopic distance (0.7 kpc, Jones et al., 2014). We suggest a distance of 1.60.6 kpc for this PN.

PN G333.900.6 (Fig. 17):

Fig. 17 shows this PN has a poor absorption spectrum. One possible absorption feature at 26 km s can be used to provide a lower limit distance 1.90.4 kpc. No upper limit distance can be derived for the PN. In fact, the previous spectroscopic distance (1.01.5 kpc) obtained by Morgan et al. (2003) agrees with our result. This PN likely has a distance of 1.90.4 kpc.

PN G352.600.1 (Fig. 18):

Two background sources (G352.50.17, G351.60.17) show reliable absorption features at the tangent point velocity, while this does not appear in the PN spectrum. This implies that the PN is in front of the tangent point. There appear H i emission and absorption at 20 km s in the spectra of the PN and H ii region G353.400.3. In fact the PN is behind the H ii region G353.400.3 (3.20.8 kpc, Tian et al. (2008)). In addition, an absorption feature at 50 km s is seen in the spectrum of G351.60.17, while H i emission is seen but no absorption at the same velocity in the PN spectrum. This implies the PN is in front of near distance of 50 km s, i.e., 5.00.3 kpc. So PN G352.600.1 is between 3.20.8 kpc and 5.00.3 kpc.

Maciel (1984) gave a lower limit 0.9 kpc for this PN by assuming a relationship between the nebular ionized mass and radius. Zhang (1995) and van de Steene & Zijlstra (1995) suggested distances of 1.40 kpc and 1.37 kpc based on the revised relation between radio surface brightness temperature and nebula radius. Therefore, we adopt 3.20.8 kpc for the PN.

PN G352.800.2 (Fig. 19):

The weak absorption features at the tangent velocity, 36 km s, and 90 km s in the H i spectrum of PN G352.800.2 have a S/N of about 3  (0.24), so we do not regard it as real absorption. The absorption feature at 20 km s is detected in the spectra of three background sources, but does not appear in the PN spectrum, implying the PN is in front of H i (3.20.8 kpc, Tian et al., 2008). In addition, the presence of clear H i emission and absence of absorption feature at 10 km s in the PN spectrum reveals an lower limit distance of 2.10.9 kpc for the PN. We conclude that the distance of the PN is between 2.10.9 kpc and 3.20.8 kpc.

The distance of the PN was also suggested by statistical methods (e.g. 0.8 kpc, Maciel (1984); 1.36 kpc, Phillips (2004); 1.53 kpc, Cahn et al. (1992); 1.39 kpc, Zhang (1995); 1.34 kpc, van de Steene & Zijlstra (1995)). Hence, we prefer the distance of 2.10.9 kpc for the PN.

4. Summary

Table 2 Final Kinematic Distances of Planetary Nebulae
PN G PN Distance limits Final distance Distance by others(Ref.) Method
Name Name kpc kpc kpc
G020.901.1 M 151 3.10.37.10.6 3.10.3 2.4(C01) surface gravity
1.75(C92),1.66(S95) statistical
1.74(Z95),2.29(S08) statistical
1.59(Ph04) statistical
2.310.75(F16) statistical
G029.000.4 A66 48 3.50.36.61.0 3.50.3 1.2(M84) statistical
1.410.43(F16) statistical
G030.200.1 - 10.90.313.20.5 10.90.313.20.5 - -
G051.500.2 KLW 1 4.71.49.50.4 4.71.49.50.4 - -
G052.101.0 - 4.71.45.40.7 4.71.45.60.8 - -
G055.500.5 M 171 4.31.58.60.4 4.31.5 1.66(C92),3.68(S08) statistical
3.17(Z95),3.17(S95) statistical
2.880.91(F16) statistical
2.90.4(G11) reddening
G069.700.0 K 355 11.070.6112.020.67 ? 3.31(C92),4.23(S08) statistical
3.26(Z95),3.09(S95) statistical
2.96(Ph04) statistical
3.541.32(F16) statistical
G070.701.2 M 360 2.51.65.00.7 5.00.7 4.51.0(B89) H i absorption
G084.903.4 NGC 7027 0.74.30.6 0.7 0.7(M84),0.64(Z95) statistical
0.27(C92),0.63(S95) statistical
0.940.27(F16) statistical
2.32.9(C01) surface gravity
0.7030.095(H93) expansion parallax
0.981.0(Z08) expansion parallax
0.940.2(M86) expansion parallax
0.880.15(M89) expansion parallax
0.680.17(M04) expansion parallax
1.15(N12) reddening
4.5(P82) H i absorption
G089.000.3 NGC 7026 3.50.6 3.50.6 2.51.0(G86) H i absorption
1.9(C92),2.35(S08) statistical
2.03(Z95),1.91(Ph04) statistical
1.94(S95) statistical
1.670.48(F16) statistical
1.570.65(K85) reddening
2.3(P83),1.5(G11) reddening
3.5(Z93),4.2(C00) surface gravity
1.9(G04) Spectroscopic parallax
G107.802.3 NGC 7354 1.20.62.80.5 1.20.6 1.50.5(G86) H i absorption
1.27(C92),1.19(Ph04) statistical
1.3(Z95),1.70(S08) statistical
1.23(S95) statistical
1.260.37(F16) statistical
1.00.15(G11) reddening
3.430.62(K85) reddening
2.1(Z93),3.2(C00) surface gravity
G138.802.8 IC 289 1.60.63.80.6 1.60.6 2.710.195(K85) reddening
1.43(C92),1.45(S08) statistical
1.68(Z95),1.18(Ph04) statistical
1.48(S95) statistical
1.880.58(F16) statistical
G147.402.3 M 14 3.60.98.71.7 3.60.9 2.23.1(C01) surface gravity
2.99(C92),3.36(S95) statistical
3.53(Z95),3.39(Ph04) statistical
6.6(S08) statistical
5.181.55(F16) statistical
3.30.35(G11) reddening
G169.700.1 IC 2120 14.7 ? 1.37(C92),1.388(S08) statistical
1.86(Z95),1.26(Ph04) statistical
G259.100.9 Hen 211 1.60.62.40.6 1.60.6 0.9(C92),1.07(Z95) statistical
0.800.24(F16) statistical
0.7(J14) Spectroscopic
G333.900.6 PMR 5 1.90.4 1.90.4 1.01.5(M03) Spectroscopic
G352.600.1 H 112 3.20.85.00.3 3.20.8 0.9(M84) statistical
1.40(Z95),1.37(S95) statistical
2.420.84(F16) statistical
G352.800.2 H 113 2.10.93.20.8 2.10.9 0.8(M84),1.36(Ph04) statistical
1.53(C92),1.39(Z95) statistical
1.34(S95) statistical
1.740.59(F16) statistical
Ref.: C01- Cazetta & Maciel (2001), C92-Cahn et al. (1992), S95-van de Steene & Zijlstra (1995), Z95-Zhang (1995)
       S08-Stanghellini et al. (2008), B89-Bally et al. (1989), N12-Navarro et al. (2012), G11-Giammanco et al. (2011)
       K85-Kaler & Lutz (1985), G86-Gathier et al. (1986a), C00-Cazetta & Maciel (2000), G04-Gruendl et al. (2004)
       P83-Pottasch (1983), Z08-Zijlstra et al. (2008), H93-Hajian et al. (1993), M84-Maciel (1984), Z93-Zhang (1993)
       Ph04-Phillips (2004), M04-Mellema (2004), M86-Masson (1986), M03-Morgan et al. (2003), M89-Masson (1989)
       J14-Jones et al. (2014),  P82-Pottasch et al. (1982), F16-Frew et al. (2016)
       –represent that we keep an open question for its distance.

We analyze the H i absorption spectra of 18 Galactic plane PNe and estimate their kinematic distances in this paper. The final results are shown in Table 2. We compare new kinematic distances of 15 PNe with the previous results determined from other methods, such as  surface gravity (5 PNe, e.g. Zhang, 1993; Cazetta & Maciel, 2000), expansion parallax (1 PN, e.g. Hajian et al., 1993; Zijlstra et al., 2008), reddening (5 PNe, e.g. Kaler & Lutz, 1985; Giammanco et al., 2011), statistical (13 PNe, e.g. Cahn et al., 1992; Zhang, 1995), H i absorption (4 PNe, e.g. Bally et al., 1989; Gathier et al., 1986a). By considering the additional distance information, we determine distances for 13 PNe with uncertainties ranging from 10 to 50. For 8 out of 13 PNe, the kinematic distances are determined with uncertainties less than . For three objects (PN G020.901.1, PN G029.000.4, PN G084.903.4)  the kinematic distances are derived with uncertainties less than 10, and for the other ten cases the kinematic distances are estimated with uncertainties less than 50. This is a significant improvement compared against most of the previous measurements with uncertainties of two or three factor smaller. For three cases the kinematic distance are derived with lower and upper distance limits (see Table 2). We do not suggest distances for PN G069.700.0 and PN G169.700.1 based on our current H i measurements only. For PN candidate PN G030.200.1, which was discussed by Anderson et al. (2011), its luminosity is 225 times stronger than the most luminous Galactic PN NGC 7027 (506 mJy at 8.6 GHz, see Zijlstra et al. 2008), so G030.200.1 might not be a PN.

In addition, our spectra have revealed that five of the PNe show larger tangent point velocities than expected from the rotation curve model when adopting IAU value of =220 km s. Three of them are located near 53. This is consistent with the previous studies in Levine et al. (2008) and Leahy et al. (2008).

We compare our distances with the previous measurements based on the data in table 2 (also see Fig. 20). We find that all other work (except statistical results, see Fig. 20, left panel) show obvious dispersion between each other, and that our distance measurements are well consistent with the most reliable method, i.e. expansion parallax. Our distance measurements are consistent with Frew et al. (2016) when considering the uncertainties, but larger than the other statistical results (see Fig. 20, middle and right panels). In order to investigate the possible effects of some PNe parameters on our measurements, we have tried to find the correlation between these parameters (e.g., radius, reddening) and the residuals which obtained by subtracting our distances from those obtained by other methods. No obvious correlation is found. A total number of 22 PNe have H i absorption measurements in the literatures. Our work significantly increases the number of Galactic PNe with H i absorption measurements and known kinematic distances.

We acknowledge support from the NSFC (11473038, 11273025, 1126114046) and also support from China’s Ministry of Science and Technology under the State Key Development Program for Basic Research (2012CB821800, 2013CB837901). D. A. Leahy is supported by a grant from the Natural Sciences and Engineering Research Council of Canada. The work has made used of data from the International Galactic Plane Survey (http://www.ras.ucalgary.ca/IGPS/).

References

  • Anantharamaiah et al. (1984) Anantharamaiah, K. R., Radhakrishnan, V., & Shaver, P. A. 1984, A&A, 138, 131
  • Anderson et al. (2011) Anderson, L. D., Bania, T. M., Balser, D. S., & Rood, R. T. 2011, ApJS, 194, 32
  • Bally et al. (1989) Bally, J., Pound, M. W., Stark, A. A., et al. 1989, ApJ, 338, L65
  • Bojičić et al. (2011) Bojičić, I. S., Parker, Q. A., Filipović, M. D., & Frew, D. J. 2011, MNRAS, 412, 223
  • Bovy et al. (2012) Bovy, J., Allende Prieto, C., Beers, T. C., et al. 2012, ApJ, 759, 131
  • Cahn et al. (1992) Cahn, J. H., Kaler, J. B., & Stanghellini, L. 1992, A&AS, 94, 399
  • Cazetta & Maciel (2000) Cazetta, J. O., & Maciel, W. J. 2000, RMxAA, 36, 3
  • Cazetta & Maciel (2001) —. 2001, Ap&SS, 277, 393
  • Ciardullo et al. (1999) Ciardullo, R., Bond, H. E., Sipior, M. S., et al. 1999, AJ, 118, 488
  • Condon & Kaplan (1998) Condon, J. J., & Kaplan, D. L. 1998, ApJS, 117, 361
  • Crovisier (1978) Crovisier, J. 1978, A&A, 70, 43
  • Dickey & Lockman (1990) Dickey, J. M., & Lockman, F. J. 1990, ARA&A, 28, 215
  • Dobbs et al. (2006) Dobbs, C. L., Bonnell, I. A., & Pringle, J. E. 2006, MNRAS, 371, 1663
  • Eisenhauer et al. (2005) Eisenhauer, F., Genzel, R., Alexander, T., et al. 2005, ApJ, 628, 246
  • Frew et al. (2016) Frew, D. J., Parker, Q. A., & Bojičić, I. S. 2016, MNRAS, 455, 1459
  • Gathier et al. (1986a) Gathier, R., Pottasch, S. R., & Goss, W. M. 1986a, A&A, 157, 191
  • Gathier et al. (1986b) Gathier, R., Pottasch, S. R., & Pel, J. W. 1986b, A&A, 157, 171
  • Giammanco et al. (2011) Giammanco, C., Sale, S. E., Corradi, R. L. M., et al. 2011, A&A, 525, A58
  • Gruendl et al. (2004) Gruendl, R. A., Chu, Y.-H., Guerrero, M. A., & Meixner, M. 2004, in Bulletin of the American Astronomical Society, Vol. 36, American Astronomical Society Meeting Abstracts, 138.05
  • Hajian et al. (1993) Hajian, A. R., Terzian, Y., & Bignell, C. 1993, AJ, 106, 1965
  • Harris et al. (2007) Harris, H. C., Dahn, C. C., Canzian, B., et al. 2007, AJ, 133, 631
  • Heyer & Terebey (1998) Heyer, M. H., & Terebey, S. 1998, ApJ, 502, 265
  • Jackson et al. (2006) Jackson, J. M., Rathborne, J. M., Shah, R. Y., et al. 2006, ApJS, 163, 145
  • Jacoby et al. (1997) Jacoby, G. H., Morse, J. A., Fullton, L. K., Kwitter, K. B., & Henry, R. B. C. 1997, AJ, 114, 2611
  • Jones et al. (2014) Jones, D., Boffin, H. M. J., Miszalski, B., et al. 2014, A&A, 562, A89
  • Kaler & Lutz (1985) Kaler, J. B., & Lutz, J. H. 1985, PASP, 97, 700
  • Kwitter et al. (2014) Kwitter, K. B., Méndez, R. H., Peña, M., et al. 2014, RMxAA, 50, 203
  • Leahy & Tian (2008) Leahy, D. A., & Tian, W. W. 2008, AJ, 135, 167
  • Leahy & Tian (2010) Leahy, D. A., & Tian, W. W. 2010, in Astronomical Society of the Pacific Conference Series, Vol. 438, The Dynamic Interstellar Medium: A Celebration of the Canadian Galactic Plane Survey, ed. R. Kothes, T. L. Landecker, & A. G. Willis, 365
  • Leahy et al. (2008) Leahy, D. A., Tian, W. W., & Wang, Q. D. 2008, AJ, 136, 1477
  • Levine et al. (2008) Levine, E. S., Heiles, C., & Blitz, L. 2008, ApJ, 679, 1288
  • Luo et al. (2005) Luo, S. G., Condon, J. J., & Yin, Q. F. 2005, ApJS, 159, 282
  • Maciel (1984) Maciel, W. J. 1984, A&AS, 55, 253
  • Masson (1986) Masson, C. R. 1986, ApJ, 302, L27
  • Masson (1989) —. 1989, ApJ, 336, 294
  • McClure-Griffiths et al. (2005) McClure-Griffiths, N. M., Dickey, J. M., Gaensler, B. M., et al. 2005, ApJS, 158, 178
  • Mellema (2004) Mellema, G. 2004, A&A, 416, 623
  • Mendez et al. (1988) Mendez, R. H., Kudritzki, R. P., Herrero, A., Husfeld, D., & Groth, H. G. 1988, A&A, 190, 113
  • Morgan et al. (2003) Morgan, D. H., Parker, Q. A., & Cohen, M. 2003, MNRAS, 346, 719
  • Napiwotzki & Schoenberner (1995) Napiwotzki, R., & Schoenberner, D. 1995, A&A, 301, 545
  • Navarro et al. (2012) Navarro, S. G., Corradi, R. L. M., & Mampaso, A. 2012, in IAU Symposium, Vol. 283, IAU Symposium, 460–461
  • Phillips (2004) Phillips, J. P. 2004, MNRAS, 353, 589
  • Pottasch (1983) Pottasch, S. R. 1983, in IAU Symposium, Vol. 103, Planetary Nebulae, ed. D. R. Flower, 391–407
  • Pottasch et al. (1982) Pottasch, S. R., Goss, W. M., Gathier, R., & Arnal, E. M. 1982, A&A, 106, 229
  • Reid et al. (2007) Reid, M. J., Brunthaler, A., Menten, K. M., et al. 2007, in IAU Symposium, ed. J. M. Chapman & W. A. Baan, Vol. 242, 348–355
  • Reid et al. (2009) Reid, M. J., Menten, K. M., Zheng, X. W., et al. 2009, ApJ, 700, 137
  • Shaver et al. (1982) Shaver, P. A., Radhakrishnan, V., Anantharamaiah, K. R., et al. 1982, A&A, 106, 105
  • Shklovskii (1956) Shklovskii, I. S. 1956, Kosmicheskoe radiolzluchenie.
  • Stanghellini et al. (2008) Stanghellini, L., Shaw, R. A., & Villaver, E. 2008, ApJ, 689, 194
  • Stil et al. (2006) Stil, J. M., Taylor, A. R., Dickey, J. M., et al. 2006, AJ, 132, 1158
  • Taylor et al. (2003) Taylor, A. R., Gibson, S. J., Peracaula, M., et al. 2003, AJ, 125, 3145
  • Terzian (1997) Terzian, Y. 1997, in IAU Symposium, Vol. 180, Planetary Nebulae, ed. H. J. Habing & H. J. G. L. M. Lamers, 29
  • Tian & Leahy (2008) Tian, W. W., & Leahy, D. A. 2008, MNRAS, 391, L54
  • Tian et al. (2008) Tian, W. W., Leahy, D. A., Haverkorn, M., & Jiang, B. 2008, ApJ, 679, L85
  • Tian et al. (2010) Tian, W. W., Leahy, D. A., & Li, D. 2010, MNRAS, 404, L1
  • Tian et al. (2007) Tian, W. W., Leahy, D. A., & Wang, Q. D. 2007, A&A, 474, 541
  • van de Steene & Zijlstra (1995) van de Steene, G. C., & Zijlstra, A. A. 1995, A&A, 293, 541
  • Viironen et al. (2009) Viironen, K., Greimel, R., Corradi, R. L. M., et al. 2009, A&A, 504, 291
  • Zhang (1993) Zhang, C. Y. 1993, ApJ, 410, 239
  • Zhang (1995) —. 1995, ApJS, 98, 659
  • Zhu et al. (2013) Zhu, H., Tian, W. W., Torres, D. F., Pedaletti, G., & Su, H. Q. 2013, ApJ, 775, 95
  • Zijlstra et al. (1990) Zijlstra, A., Pottasch, S., & Bignell, C. 1990, A&AS, 82, 273
  • Zijlstra et al. (2008) Zijlstra, A. A., van Hoof, P. A. M., & Perley, R. A. 2008, ApJ, 681, 1296
Figure 2.— 1420 MHz continuum image of PN G020.901.1 and its background sources (top left), and the H i spectra of PN G020.901.1 (bottom left), G021.30.63 (top right) and G021.50.89 (bottom right). The map has superimposed contours (20,50,130 K) of 1420 MHz continuum emission. The dotted horizontal lines in the lower panel of the PN spectrum show the 3 noise level. This description applies for all the spectra of PNe and background sources from Fig. 2 to Fig. 19.
Figure 3.— 1420 MHz continuum image of PN G029.000.4, and its background sources (top left), and the H i spectra of PN G029.000.4 (bottom left), G028.80.18 (top right), and G029.000.5 (bottom right). The H i spectra of G028.80.23 is listed in appendix Fig. 21. The map has superimposed contours (30,50,120 K) of 1420 MHz continuum emission.
Figure 4.— 1420 MHz continuum image of PN G030.200.1 and its nearby background source (top left), and the H i spectra of PN G030.200.1 (bottom left), G030.540.02 (top right), and G030.690.26 (bottom right), The H i spectra of G029.930.05 and G029.960.02 are listed in appendix Fig. 21. The map has superimposed contours (65,125,230 K) of 1420 MHz continuum emission.
Figure 5.— 1420 MHz continuum image of PN G051.500.2 and its nearby background sources (top left), and the H i spectra of PN G051.500.2 (bottom left), G051.700.8 (top right), and G050.600.3 (bottom right). The H i spectra of G050.950.85 is shown in appendix Fig. 21. The map has superimposed contours (15,25,60 K) of 1420 MHz continuum emission.
Figure 6.— 1420 MHz continuum image of PN G052.101.0, and its background sources (top left), and the H i spectra of PN G052.101.0 (bottom left), G052.20.75 (top right) and G052.70.3 (bottom right). The map has superimposed contours (15,35,55 K) of 1420 MHz continuum emission.
Figure 7.— 1420 MHz continuum image of PN G055.500.5 and its nearby background sources (top left), and the H i spectra of PN G055.500.5 (bottom left) , G055.501.1 (top right), and G055.901.2 (middle right). The H i spectra of G055.700.2 is shown in appendix Fig. 21. The map has superimposed contours (8,15,35 K) of 1420 MHz continuum emission.
Figure 8.— 1420 MHz continuum image of PN G069.700.0, and its nearby background sources (top left), and the H i spectra of PN G069.700.0 (bottom left), G068.70.27 (top right) and G070.10.96 (bottom right). The map has superimposed contours (5,12,32 K) of 1420 MHz continuum emission.
Figure 9.— 1420 MHz continuum image of PN G070.701.2, and its background sources (top left), and the H i spectra of PN G070.701.2 (bottom left), G071.201.4 (top right), and G070.601.38(bottom right). The H i spectra of G070.690.63 is listed in appendix Fig. 21. The map has superimposed contours (15,25,50 K) of 1420 MHz continuum emission.
Figure 10.— 1420 MHz continuum image of PN G084.903.4 and it nearby background sources (top left), and the H i spectra of PN G084.903.4 (bottom left), G085.103.1 (top right), G084.402.9 (bottom right). The map has superimposed contours (15,50,100 K) of 1420 MHz continuum emission.
Figure 11.— 1420 MHz continuum image of PN G089.000.3 and its nearby background sources (top left), and the H i spectra of PN G089.000.3 (bottom left) , G088.800.9 (top right), and G089.600.9 (bottom right). The H i spectra of G088.4600.0 is shown in appendix Fig. 21. The map has superimposed contours (15,25,35 K) of 1420 MHz continuum emission.
Figure 12.— 1420 MHz continuum image of PN G107.802.3 and its nearby background sources(top right) , and the H i spectra of PN G107.802.3 (bottom left), G108.702.57(top right). The map has superimposed contours (20,50,100 K) of 1420 MHz continuum emission.
Figure 13.— 1420 MHz continuum image of PN G138.802.8 and G138.802.4 (top left), and the H i spectra of PN G138.802.8 (bottom left), G138.802.14 (top right). The map has superimposed contours (15,25,35 K) of 1420 MHz continuum emission.
Figure 14.— 1420 MHz continuum image of PN G147.402.3, and its background sources (top left), and the H i spectra of PN G147.402.3 (bottom left), G146.62.69 (top right) and G147.902.6 (bottom right). The map has superimposed contours (15,55 K) of 1420 MHz continuum emission.
Figure 15.— 1420 MHz continuum image of PN G169.700.1 and its background sources (top left), and the H i spectra of PN G16900.1 (bottom left), G169.080.25 (top right) and G170.30.23 (bottom right). The map has superimposed contours (15,50,100 K) of 1420 MHz continuum emission.
Figure 16.— 1420 MHz continuum image of PN G259.100.9, and its nearby background sources (top left), and the H i spectra of PN G259.100.9 (bottom left), G257.900.8 (top right) and G257.900.6 (bottom right). The map has superimposed contours (0.03,0.15,0.5 Jy) of 1420 MHz continuum emission.
Figure 17.— 1420 MHz continuum image of PN G333.900.6, and its background sources (top left), and the H i spectra of PN G333.900.6 (bottom left), G333.700.3 (top right) and G332.900.7 (bottom right). The map has superimposed contours (0.1,0.18,1.0 Jy) of 1420 MHz continuum emission.
Figure 18.— 1420 MHz continuum image of PN G352.600.1 and its nearby background sources (top left), and the H i spectra of PN G352.600.1 (bottom left) , G352.50.17 (top right), and G351.60.17 (bottom right). The H i spectra of G353.400.3 is shown in Fig. 19. The map has superimposed contours (0.15,0.35,1.0 Jy) of 1420 MHz continuum emission.
Figure 19.— 1420 MHz continuum image of PN G352.800.2 and its nearby background sources (top left), and the H i spectra of PN G352.800.2 (bottom left) , G352.800.1 (top right), and G353.400.3 (bottom right). The H i spectra of G352.50.17 is shown in Fig. 18. The map has superimposed contours (0.15,0.35,1.0 Jy) of 1420 MHz continuum emission.
Figure 20.— Left panel: the correlation between our work and all other work (except statistical method). Middle panel: the correlation between our work and Frew et al. (2016). Right panel: the correlation between our work and all statistical results.
     
     
Figure 21.— Nearby background sources are also used to measure the PN kinematic distances, the dotted horizontal lines in the lower panel of the background sources show the 3 noise level.
Comments 0
Request Comment
You are adding the first comment!
How to quickly get a good reply:
  • Give credit where it’s due by listing out the positive aspects of a paper before getting into which changes should be made.
  • Be specific in your critique, and provide supporting evidence with appropriate references to substantiate general statements.
  • Your comment should inspire ideas to flow and help the author improves the paper.

The better we are at sharing our knowledge with each other, the faster we move forward.
""
The feedback must be of minimum 40 characters and the title a minimum of 5 characters
   
Add comment
Cancel
Loading ...
267030
This is a comment super asjknd jkasnjk adsnkj
Upvote
Downvote
""
The feedback must be of minumum 40 characters
The feedback must be of minumum 40 characters
Submit
Cancel

You are asking your first question!
How to quickly get a good answer:
  • Keep your question short and to the point
  • Check for grammar or spelling errors.
  • Phrase it like a question
Test
Test description