text stringlengths 128 2.05k |
|---|
Time development of the temperatures is shown in Figure 5. The electron temperature rises rapidly up to about [MATH] when the Buneman instability grows, while at this phase the proton temperature does not rise so much. At about |
[MATH] , the proton temperature begins to rise by the growth of the ion two-stream instability but the electron temperature is kept at almost the same because this instability occurs between two ion beams and the energy density of the electric field is nearly 100 times smaller than the thermal energy density of electro... |
becomes about 10. For the magnetized case, [MATH] becomes about 7. Although it is not explicitly shown in this paper, the proton distribution has a large anisotropy. Only the proton temperature of the [MATH] -direction rises up, but that of the |
[MATH] -direction is kept to be almost constant. Figure 7 shows the energy distribution of electrons at the end of the simulation. The bold and thin curves represent non-mangetized and magnetized cases, respectively. It is noted that no high energy tail is seen. Even when there exists a magnetic field, electrons are no... |
[MATH] . As discussed in Ohira & Takahara ( 2007 , at the end of simulation, the electron temperature becomes [MATH] . These results are consistent with our previous result (Ohira & Takahara, 2007 |
Discussion Now we discuss the final outcome of the ion two-stream instability. It becomes unstable when two conditions are satisfied; one is the resonance condition, [MATH] and the other is that the wave length be between the ion Debye length and the electron Debye length. Thus, the ion two-stream instability becomes s... |
[MATH] at the foot region in high Mach number perpendicular shocks. Of course, because the proton temperature of the drift direction is still cold in the present simulation, we must check the isotropilazation process of ion velocity distribution by doing longtime full PIC-simulations. |
As for the electrons, the electron temperature in the foot region is also about [MATH] . In the later stage, the growth of the two-stream instability dominates over the ion acoustic instability and little electron heating occurs. Hence, as mentioned in Ohira & Takahara ( 2007 if other electron heating mechanisms do not... |
[EQUATION] where we assume that the compression ratio is 4. This has a very important implication for the electron heating process of the SNR shocks. The proton temperature in the downstream is |
[MATH] , hence the ratio of two temperatures is [EQUATION] This value is close to the observed value as long as the shock velocity |
[MATH] is larger than [MATH] (Adelsberg et al., 2008 . Namely, we expect that the overheating problem of electrons raised by Cargill & Papadopoulos ( 1988 can be solved by the ion two-stream instability. |
In this paper, we prepare three ion beams as the initial condition. We have also performed simulations for other initial conditions such that there exist upstream electrons, upstream and reflected protons. Electrons and reflected protons have drift velocities to satisfy the vanishing current condition. This situation c... |
Our simulation does not include electromagnetic modes. In the linear stage of the Buneman and ion two-tream instabilities, the effects are negligible because the growth rates of electromagnetic modes are smaller than those of electrostatic modes for [MATH] In the nonlinear stage, electromagnetic modes may be important.... |
[MATH] is about 100. These two features may lead to magnetic field amplification and accompanying particle acceleration and heating in the shock foot region. We will make full-PIC simulations in future work to investigate these issues. |
Summary We performed linear analysis of two-dimensional electrostatic modes and electrostatic two-dimensional PIC simulations with the real proton electron mass ratio to investigate the time evolution of electrostatic waves in the foot region of collisionless shocks with a high Mach number. We consider only the foot re... |
We are grateful to T. Tsuribe, T. Umeda, R. Yamazaki, T. Kato, M. Hoshino, T. Terasawa, S. Matsukiyo for discussions and suggestions especially for providing useful guidance and information in doing numerical simulations and for the nature of the ion two-stream instability. This work is partly supported by Scientific R... |
# Source: arxiv 0808.3201 # Title: High Angular Resolution Observations at 7-mm of the Core of the Quadrupolar HH 111/121 Outflow # Sections: all # Downloaded: 2026-03-02T07:57:59.548400+00:00 |
High Angular Resolution Observations at 7-mm of the Core of the Quadrupolar HH 111/121 Outflow Abstract We present sensitive, high angular resolution ( [MATH] ) VLA continuum observations made at 7 mm of the core of the HH 111/121 quadrupolar outflow. We estimate that at this wavelength the continuum emission is domina... |
To appear in The Astronomical Journal Introduction It is generally accepted that most stars form in binary or multiple systems (Lada & Lada 2003). Furthermore, in the case of low and intermediate-mass stars it is also known that the process occurs with the presence of an accretion disk and a collimated outflow. From th... |
One of the most interesting cases of a binary source that is known to exhibit independent outflows, most probably associated with each of the components of the binary, is HH 111 (Reipurth et al. 1999). Located in Orion at a distance of 414 pc (Menten et al. 2007), the optical HH 111 jet was discovered by Reipurth (1989... |
[MATH] years of its lifetime. Near-infrared observations (Gredel & Reipurth 1993; 1994) revealed a second bipolar flow, named HH 121, that emerges from about the same position as the optical outflow, and is aligned approximately in the north-south direction (at a PA of [MATH] ). This result suggested the presence of a ... |
At the center of the quadrupolar outflow is the source IRAS 05491+0247 = VLA 1, a suspected class I binary with a total luminosity of about 25 L |
(e.g. Stapelfeldt & Scoville 1993, Yang et al. 1997). To advance in our understanding of this source a high angular resolution image at millimeter wavelengths was needed to compare with the information available for the quadrupolar outflow. |
Observations The 7 mm continuum observations were made in the A configuration of the VLA of the NRAO , during 2006 February 10 and 15. The central frequency observed was 43.34 GHz and we integrated on-source for a total of approximately 5 hours. The absolute amplitude calibrator was 1331+305 (with an adopted flux densi... |
and 30 , for the first and second epoch, respectively, indicating good weather conditions. The phase center of the observations was at |
[MATH] The data were acquired and reduced using the recommended VLA procedures for high frequency data, including the fast-switching mode with a cycle of 120 seconds. The effective bandwidth of the observations was 100 MHz. |
Analysis 3.1 7 mm Data In Figure 1 we show the 7 mm image of the core of the HH 111/121 quadrupolar outflow. An unusual structure is evident in the image. The structure can be described as two overlapping, elongated sources aligned in the plane of the sky and approximately perpendicular to each other. We have fitted th... |
For the purpose of comparison, we also show in Figure 1 the 3.6 cm continuum image obtained from the VLA data presented by Reipurth et al. (1999). These data have been recalibrated and the position of their phase calibrators updated by displacements of order |
[MATH] to the most recent values in the VLA calibrator catalog to allow accurate astrometric comparison with the 7 mm image. As first discussed by these authors, the 3.6 cm VLA image is suggestive of a quadrupolar jet, with a common origin within [MATH] |
[MATH] 40 AU). The main jet is aligned approximately in the east-west direction (that with a PA of [MATH] is taken to be the exciting agent of the extended optical HH 111 flow), while the second jet is aligned approximately in the north-south direction (that with a PA of [MATH] |
is taken to be the exciting agent of HH 121). The error in the position angle of the north-south jet was obtained from our reanalysis of the Reipurth et al. (1999) data. The quadrupolar structure of the 3.6 cm emission is more evident in the maximum entropy reconstruction of the image shown by Reipurth et al. (1999). F... |
We are then faced with a question: since the position angles of the two nearly perpendicular structures observed at 7 mm are similar to those observed at 3.6 cm, are we seeing at 7 mm two jets, two disks, or a jet and a disk? To address these interpretations, we first discuss additional continuum observations of the re... |
3.2 Flux Densities at Other Wavelengths We searched in the literature and in the VLA archives for additional data points of the continuum flux density of this source. In Table 2 we present a summary of the total flux densities obtained for the region. The observations are not taken simultaneously and if time variations... |
The total continuum flux density at 7 mm is about 40% larger than the addition of the individual flux densities given in Table 1. This difference results from the presence of faint, extended 7 mm emission that is not accounted for in the individual Gaussian fits. Analysis of the residual (with the Gaussian fits removed... |
[MATH] 30 GHz. We have fitted the data points with the sum of two power laws of the form: [EQUATION] where the first term is intended to represent the contribution of free-free emission from the ionized outflow and the second term is intended to represent the contribution of dust emission from the disks. Since we have ... |
[MATH] = 3.6 mJy. Under this interpretation, the 8.44 GHz emission is clearly dominated by free-free, with only [MATH] 6% of dust contribution. On the other hand, the 43.34 GHz emission is dominated by dust, with a [MATH] 30% contribution from free-free. Following Rodríguez, Zapata, & Ho (2007) and Hunter et al. (2006)... |
3.3 Two jets? The excess of 7-mm emission with respect to the value expected from the extrapolation of the centimeter measurements rules out the possibility that at 7-mm we are simply observing two jets since we have estimated that a significant fraction ( [MATH] 70%) of the 7-mm emission is due to dust. However, we ca... |
3.4 Two disks? This possible interpretation is suggested by the fact that at 3.6 cm the structure with the larger flux density is the east-west one, while at 7 mm this is true for the north-south structure (see Fig. 1 and Table 1). Rodríguez et al. (2008), from a comparison between the momentum rate in the molecular ou... |
This interpretation faces, however, three difficulties. The first difficulty is that the axes of the proposed disk-jet structures are not, as expected, nearly perpendicular. The east-west structure at 3.6 cm has a PA of [MATH] , while the north-south structure at 7 mm has a PA of [MATH] having a relative angle of [MATH... |
The second difficulty is related to the stability of the proposed binary disk system. From Table 1, we estimate that the centroids of the two 7 mm structures are separated by [MATH] or [MATH] 15 [MATH] 6 AU at a distance of 414 pc. We expect the disks in a binary system to be truncated at radii of order a fraction of t... |
[MATH] 15 AU (assuming that the observed separation is comparable to the true separation). In contrast, the observed radii (see Table 1) are significantly larger, in the order of 35 AU. |
The final difficulty is that, if we assume masses of order 1 [MATH] for the stars in the binary system, an orbital period of order 40 years is expected for a separation of [MATH] 15 AU. The expected timescale in which strongly misaligned binary disks should be brought into rough alignment by tidal torques is about 20 o... |
These last two difficulties are mitigated if we consider that the real separation is much larger than the projected one. A physical separation of 105 AU would be consistent with the values of 35 AU for tidally truncated radii. The orbital period would now be about 800 years and the timescale for alignment |
[MATH] years, consistent with the lifetime of the system. However, if we define the physical separation as [MATH] , the probability of observing it at a projected separation of [MATH] or smaller is: |
[EQUATION] that for [MATH] = 15 AU and [MATH] =105 AU, gives [MATH] We conclude that either we are observing the binary at an unlikely orientation, that disks in binary systems are more stable and independent than previously thought, or that the interpretation is incorrect. |
3.5 One jet and one disk? This final interpretation implies that at 7-mm we are seeing a north-south structure dominated by dust emission that traces a disk and an east-west structure that could be related with the jet that powers the optical HH 111 outflow. A major advantage with this interpretation is that the struct... |
[MATH] , very close to perpendicularity. The east-west structure has a flux density of 0.7 [MATH] 0.2 mJy at 3.6 cm and of 1.4 [MATH] 0.3 mJy at 7-mm. This results in a spectral index of 0.4 [MATH] 0.2, that is consistent with the value expected for a thermal jet (e. g. Anglada 1996; Eislöffel et al. 2000). |
However, this interpretation also presents some difficulties. The east-west structure at 3.6 cm has a position angle of [MATH] , while the east-west structure at 7 mm has a position angle of [MATH] . In other words, the two structures are not nearly parallel, as expected if the 3.6 cm emission were the larger scale cou... |
Conclusions Our main conclusions follow: 1) Our high angular resolution ( [MATH] ) VLA continuum 7 mm observations of the core of the HH 111/121 quadrupolar outflow reveal a structure that can be described as two overlapping, elongated sources that appear approximately perpendicular to each other in the plane of the sk... |
2) We discuss possible interpretations for this structure and conclude that the most viable ones are that we are observing two orthogonal disks around separate protostars or a disk with a perpendicular jet. Both intepretations have advantages and disadvantages, and high angular resolution spectroscopic millimeter obser... |
We thank an anonymous referee for valuable suggestions. LFR acknowledges the support of CONACyT, México and DGAPA, UNAM. JMT and GA are supported by the MEC AYA2005-05823-C03 grant (co-funded with FEDER funds). GA also acknowledges support from Junta de Andalucía. References |
# Source: arxiv 0808.3226 # Title: A Molecular Line Survey of the Highly Evolved Carbon Star CIT 6 # Sections: all # Downloaded: 2026-03-02T07:58:00.762483+00:00 |
A Molecular Line Survey of the Highly Evolved Carbon Star CIT 6 Abstract We present a spectral line survey of the C-rich envelope CIT 6 (catalog ) in the |
[MATH] 2 mm and 1.3 mm bands carried out with the Arizona Radio Observatory (ARO) 12 m telescope and the Heinrich Hertz Submillimeter Telescope (SMT). The observations cover the frequency ranges of 131–160 GHz, 219–244 GHz, and 252–268 GHz with typical sensitivity limit of [MATH] mK. A total of 74 individual emission f... |
and IRC+10216 (catalog ) and those in the bright proto-planetary nebula CRL 618 (catalog ) . The implication on the circumstellar chemistry is discussed. |
ISM: molecules — radio lines: stars — line: identification — stars: AGB and post-AGB — stars: circumstellar matter — stars: individual (CIT 6) — surveys |
Introduction The late stages of stellar evolution from the asymptotic giant branch (AGB) to planetary nebulae (PN) are now recognized as an active period of chemical synthesis of molecules. The detection and analysis of millimeter wave molecular emission lines are fundamental to the understanding of the physical condit... |
Recent improvement in telescope design and receiver performance enable us to detect new molecular emission with a higher sensitivity, and thus with the possibility of shedding new light on circumstellar chemistry. The most frequently investigated C-star envelope is IRC+10216 (catalog ) which is one of the richest molec... |
IRC+10216 (catalog ) is a chemically unique late-type star. To settle this question, we require systematic surveys of molecular line emission from other C-star envelopes. In the present study, we report a spectral-line survey of the C-star envelope CIT 6 (catalog ) at millimeter wavelengths. This allows us to compare t... |
CIT 6 (catalog ) RW LMi, GL 1403, IRC+30219, IRAS 10131+3049 (catalog ) ) was first discovered during the Caltech 2- [MATH] m sky survey and was among the 14 very red infrared-bright optical-faint sources found (Ulrich et al., 1966 |
CIT 6 (catalog ) is characterized by its very low color temperature, implying that the star is surrounded by a very thick dust envelope and has been identified as a long-period variable with a period of about 628 days (Alksnis, 1995 From the period-luminosity relation, Cohen & Hitchon ( 1996 estimated the distance of C... |
[MATH] pc, which is slightly more distant than IRC+10216 (catalog ) , which has a distance of between [MATH] pc (Groenewegen et al., 1998 and [MATH] pc (Lucas & Guélin, 1999 |
CIT 6 (catalog ) is believed to be more evolved and has a lower mass loss rate compared to IRC+10216 (catalog ) (see Fukasaku et al., 1994 , e.g.) |
The large polarization found in the visible and infrared wavelengths implies that the distribution of circumstellar material around the star is asymmetric (Kruszewski, 1968 ; Dyck et al., 1971 Multi-wavelength imaging observations have been performed to study the structure of the nebula around CIT 6 (catalog ) The opti... |
obtained by the Keck-I telescope have revealed a bipolar dust envelope and an elongated component with time-variable asymmetry (Monnier et al., 2000 Several scattering arcs were revealed by the HST-NICMOS imaging polarimetry (Schmidt et al., 2002 These arcs are nearly concentric and extend to large stellar radii. Mid-I... |
Lagadec et al. ( 2005 using the ESO 3.6-m telescope. A cometary-like feature was revealed in their 9.7 [MATH] m image. There have been several observations of molecular lines in |
CIT 6 (catalog ) at millimeter wavelength. Henkel et al. ( 1985 reported observations of a few molecular lines in CIT 6 (catalog ) and IRC+10216 (catalog ) between 18 and 150 GHz. They found that relative abundances of observed molecules in the two sources have no significant differences. Using the Nobeyama 45 m radio ... |
Fukasaku et al. ( 1994 observed a few transitions in the frequency ranges between 39–47 GHz and 85–91GHz in a sample of evolved stars including CIT 6 (catalog ) and found that the abundance of HNC increases with the evolutionary stage of the stars. |
Bujarrabal et al. ( 1994 presented observations of 10 molecular transitions in C-rich and O-rich circumstellar envelopes including CIT 6 (catalog ) |
with the IRAM 30 m radio telescope at 1.3 mm, 2 mm, and 3 mm windows. A recent molecular line survey was presented by Woods et al. ( 2003 using the SEST 15 m and Onsala 20 m telescopes. They found that |
CIT 6 (catalog ) stands out from the other C-rich envelopes due to its high CN/HCN ratio and low HNC/HCN ratio. To date, the molecular species positively detected in CIT 6 (catalog ) |
at millimeter wavelengths include CO, 13 CO, CN, 13 CN, CS, SiO, SiS, 29 Si 32 S, H, SiC , HCN, H 13 CN, HNC, C N, HC N, HC 13 CCN, HCC 13 CN, and HC N. |
In this paper, we present the first systematical line survey of CIT 6 (catalog ) at the 2 mm and 1.3 mm windows, using the Arizona Radio Observatory (ARO) 12 m telescope and the Heinrich Hertz Submillimeter Telescope (SMT). The observations are described in Sec. 2. In Sect. 3 we present the identifications and abundanc... |
Observations and data reduction The observations were carried out in beam switching mode with an azimuth beam throw of 2 during the period from 2005 April to 2006 September. Pointing was checked by observations of a planet every 2 hours. The 131–160 GHz (2 mm window) spectra were obtained with the ARO 12 m telescope at... |
[MATH] , were obtained using standard vane calibration. [MATH] calibration error was obtained from a few strong lines detected in different spectrometers and different epochs. The main beam brightness temperatures were derived through |
[MATH] and [MATH] , for the 12 m and the SMT data, respectively, where [MATH] is the corrected beam efficiency ( [MATH] see the ARO 12 m manual for its definition) and [MATH] the beam efficiency ( [MATH] ). Both telescopes have a large beam size, covering the whole emission region. |
The CLASS software package in GILDAS was used to reduce the spectra. After discarding the bad scans which are seriously affected by bandpass irregularities, we co-added the spectra from individual scans. The baseline was fitted with a low-order polynomial. In order to improve the signal-to-noise ratios, the spectra wer... |
[MATH] mK in main beam brightness temperature units and a spectral resolution of [MATH] km/s. Since each line has been observed by two different spectrometers, we can reduce the uncertainties caused by ripples and bad channels. |
Results 3.1 Line identification and measurement A total of 74 individual features were detected in our survey, including some less than certain detections. Line identification is mainly based on the JPL catalog |
(Pickett et al., 1998 and the Cologne database for molecular spectroscopy (CDMS, Müller et al., 2001 2005 which give the molecular line frequencies based on theoretical calculations. We also used the NIST Recommended Rest Frequencies for Observed Interstellar Molecular Microwave Transitions , which provides the molecul... |
CRL 618 (catalog ) by He et al. ( 2008 Cernicharo et al. ( 2000 , and Pardo et al. ( 2007 for reference. The complete spectra obtained with the ARO 12 m telescope and the SMT 10 m telescope are plotted in Figs. and along with identified lines marked. Figs. and give the detected molecular line profiles. Note that the tw... |
Five faint features remain unidentified and they are listed in Table . Comparing with the unidentified line listing in the NIST frequency table, we find that the 148444, 255940, and 265936 MHz lines have no previous recorded detections elsewhere, and the 257035 and 262255 MHz may have corresponding U lines at 257015 an... |
A detailed description of the molecules detection is given below. [MATH] The [MATH] –1 transitions of CO, 13 CO, and C 17 O were detected at the 1.3 mm window. Fig. clearly shows that the shape of the CO line differs from that of the 13 CO line. The CO line shows a parabolic profile, while the 13 CO line has a double-p... |
respectively, a factor of [MATH] larger than our results. As the beam size of the IRAM telescope is about half of that of the SMT, the discrepancy of the CO intensity can be explained with different beam dilution effects. Hence, we can conclude that the variation of CO intensity is relatively small (within 10 [MATH] ) ... |
[MATH] SiC has been detected by Woods et al. ( 2003 in the spectra of CIT 6 (catalog ) through the SiC (5 0,5 –4 0,4 )) transition at 115.382 GHz. In our line survey, a number of SiC transitions were prominently detected at the 2 mm and 1.3 mm windows. These lines have a similar profile with an average linewidth of |
[MATH] km s -1 . We also detected two faint 29 SiC transition although their intensities are only at a 2–3 [MATH] noise level. We cannot find previous papers reporting on the detections of these SiC |
and 29 SiC transitions tabulated in Table [MATH] CIT 6 (catalog ) is characterized by bright CN emission. The frequencies of three CN (2–1) fine-structure groups lie in the region of the SMT spectrum. All of them were clearly seen in Fig. . The three CN (2–1) fine-structure groups consist of 18 hyperfine structure comp... |
Bachiller et al. ( 1997 carried out a survey of CN (2–1) and (1–0) emission in a sample of evolved stars. They detected the strongest two CN (2–1) groups in CIT 6 (catalog ) . Their observations suggests the intensity ratio of high- and low-frequency fine-structure groups to be 1.5, in excellent agreement with our resu... |
[MATH] Strong CS (3–2) emission was detected in the 2 mm window. This line had previously been discovered by Bujarrabal et al. ( 1994 |
and Henkel et al. ( 1985 We also clearly detected its isotopic transitions, 13 CS (3–2, 5–4) and 34 S (3–2, 5–4). The faint C 33 S (5–4) emission was only marginally discovered. The CS (5–4) transition at 244.9 GHz does not lie in the frequency region observed in the work because of a gap between 244.5–252.5 GHz in the... |
[MATH] The [MATH] –5 and [MATH] –4 transitions of SiS in CIT 6 (catalog ) have previously been observed by many researchers (Henkel et al., 1985 ; Bujarrabal et al., 1994 ; Woods et al., 2003 ; Schöier et al., 2007 In this work, three SiS transitions with higher [MATH] |
(8–7, 13–12, and 14–13) were clearly detected with an average linewidth of [MATH] km s -1 [MATH] SiO emission in this carbon star has been extensively studied. The transitions observed by previous studies include [MATH] –1, 3–2, 5–4, and 8–7 (Bujarrabal et al., 1994 ; Bieging et al., 2000 ; Woods et al., 2003 ; Schöier... |
[MATH] The [MATH] –0 transition of C H in this object has been detected by Fukasaku et al. ( 1994 . The [MATH] –2 transition lies in our surveyed frequency range. The rotation transition is split in six hyperfine-structure lines grouped in three fine-structure groups, all of which were detected at the 2 mm window. The ... |
[MATH] The [MATH] -2 transitions of HCN and H 13 CN were clearly detected. The HCN (3–2) transition is the second brightest line after the CO (3–2) transition in our survey. This line was first observed by Bieging et al. ( 2000 using the SMT, who obtained an integrated intensity of 43.1 K km s -1 , in excellent agreeme... |
[MATH] –2 transitions are below the [MATH] noise level. In CIT 6 (catalog ) , HCN is the only species with detected vibrationally excited transitions. Fig. shows that these vibrationally excited lines are probably narrower than the HCN (3–2) line. Discarding the uncertain detection of the [MATH] |
[MATH] –2 transitions and the [MATH] [MATH] –2 transition which is partially blended with the HCN (3–2) line, we obtain the average width of the vibrationally excited lines of HCN to be 14.2 K km s -1 The narrow linewidth of the vibrationally excited lines suggests that they might arise from the hot inner region with l... |
[MATH] Fukasaku et al. ( 1994 and Woods et al. ( 2003 observed the C N (11–10 a,b) transitions in CIT 6 (catalog ) Both lines are relatively weak. Due to fine-structure interactions, every rotational transition of C N is split into doublets of similar intensity. There are 12 C N transitions present in our survey range ... |
[MATH] To our knowledge, C H has not been detected in CIT 6 (catalog ) before this work. Fukasaku et al. ( 1994 and Woods et al. ( 2003 |
estimated the intensity upper-limits of the H (10–9 a,b) transitions, which indicate that C H emission in this object is relatively weak. Analogous to that of C N, every rotational transition of C H is split into two components with a similar intensity. There are 12 favorable lines of C H present in the frequency range... |
[MATH] . Seven HC N transitions from [MATH] –14 to [MATH] –28 are in the frequency range of our survey. All of them were prominently detected with |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.