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Finally. in Sec. | Finally, in Sec. |
5 we conclude with a summary and a brief discussion of our results in the context of their possible importance for (he angular momentum redistribution within solar-(wpe stars and the solution of the problem of the | 5 we conclude with a summary and a brief discussion of our results in the context of their possible importance for the angular momentum redistribution within solar-type stars and the solution of the problem of the |
Alternatively. the wind morphology and mass-loss mechanism could be set by the initial conditions such as angular momentum and magnetic fields. | Alternatively, the wind morphology and mass-loss mechanism could be set by the initial conditions such as angular momentum and magnetic fields. |
To distinguish between the different scenarios to explain (he dichotomy in wind morphology will require a much larger sample of massive YSOs to be resolved in (heir radio continuum. | To distinguish between the different scenarios to explain the dichotomy in wind morphology will require a much larger sample of massive YSOs to be resolved in their radio continuum. |
This is a task lor the EVLA and e-AJERLIN arravs. | This is a task for the EVLA and e-MERLIN arrays. |
It would also be advantageous to acquire complementary velocity resolved IR IE I line profiles. | It would also be advantageous to acquire complementary velocity resolved IR H I line profiles. |
These vield information on the acceleration of the gas close to the source. | These yield information on the acceleration of the gas close to the source. |
Unfortunately. most of the jet sources are too deeply embedded {ο use the traditional Brackett series lines and longer wavelength probes vill likely have to be deploved. | Unfortunately, most of the jet sources are too deeply embedded to use the traditional Brackett series lines and longer wavelength probes will likely have to be deployed. |
Combined with multi«limensional modelling of both the line and continuum data (hese data should (hen allow the physics behind the ionized mass-loss in massive YSOs to be unlocked. | Combined with multi-dimensional modelling of both the line and continuum data these data should then allow the physics behind the ionized mass-loss in massive YSOs to be unlocked. |
MERLIN is a National Facility operated by (he University of Manchester on behalf of PPARC. | MERLIN is a National Facility operated by the University of Manchester on behalf of PPARC. |
The stall at Jodrell Bank Observatory are thanked for their assistance in making the observations wilh MERLIN. | The staff at Jodrell Bank Observatory are thanked for their assistance in making the observations with MERLIN. |
In particular. Drs Simon Garringtou aud Tom Muxlow provided invaluable help with the data reduction. | In particular, Drs Simon Garrington and Tom Muxlow provided invaluable help with the data reduction. |
Useful discussions on the interpretation of the data were held with Dr Janet Drew. | Useful discussions on the interpretation of the data were held with Dr Janet Drew. |
The referee is acknowledged lor improving the clarity of the paper. | The referee is acknowledged for improving the clarity of the paper. |
been removed (Alvesetal.2007). | been removed \citep{alv07}. |
. We have used the same criterion iu our study. (Forbrichetal.2009). | We have used the same criterion in our study \citep{for09}. |
. For purposes other than define the On-core regions. we use the total extinction nip computed by Lombardictal.(2006). | For purposes other than defining the on-core regions, we use the total extinction map computed by \citet{lom06}. |
.. The pixel size of the extinction maps is 30%, | The pixel size of the extinction maps is $30''$. |
Looking for possible class IIT objects. we select X-ray sources with 2MLASS counterparts in these regions. requiring A& baud detections. | Looking for possible class III objects, we select X-ray sources with 2MASS counterparts in these regions, requiring $K_S$ band detections. |
We then use their X-ray properties as well as TRAC and MOPS data to better characterize them. | We then use their X-ray properties as well as IRAC and MIPS data to better characterize them. |
Finally, to further coustrain any population of class TID sources. we combine the N-rayv source selection with detections at 21 gan from our sensitive. Spitzer--MIPS study (Forbrichctαἱ. 2009). | Finally, to further constrain any population of class III sources, we combine the X-ray source selection with detections at 24 $\mu$ m from our sensitive -MIPS study \citep{for09}. |
. To cover the eutire Pipe Nebula complex. we make use of the ROSAT Al-Sky Survey in the form ofthe Bright Source Catalogue (Voges1999) and the Faint Source Catalogue (Vosges(al. 2000). | To cover the entire Pipe Nebula complex, we make use of the ROSAT All-Sky Survey in the form of the Bright Source Catalogue \citep{vog99} and the Faint Source Catalogue \citep{vog00}. |
. The observatious for this survey were carried out in 1990/91 with the Position-Seusitive Proportional Counter (PSPC). in the energy rauge of 0.19.1 keV. The X-ray satellite has observed he Pipe Nebula region several times. | The observations for this survey were carried out in 1990/91 with the Position-Sensitive Proportional Counter (PSPC), in the energy range of 0.1–2.4 keV. The X-ray satellite has observed the Pipe Nebula region several times. |
Here. we ialvze hnree particular observations. targetiug he prominent extinction cores 559. Fest1577... and. 668. | Here, we analyze three particular observations, targeting the prominent extinction cores 59, FeSt, and 68. |
The latter reeiou was observed or Sl ksec on September 27. 2002 (07:19.21:00 UT. nediau filter. observation ID 0152750101). followed * observations of the two other regious ou August 29. 2001: Fest 1-157 (06:1919:53 UT. 53 ksec. thin filter. observation ID 0206610201) and Bho (21:5310:11(11) UT. 19. ksec. thin filter. observation ID 0206610101). | The latter region was observed for 51 ksec on September 27, 2002 (07:19–21:00 UT, median filter, observation ID 0152750101), followed by observations of the two other regions on August 29, 2004: Fest 1-457 (06:19–19:53 UT, 53 ksec, thin filter, observation ID 0206610201) and 59 (21:53–10:14(+1) UT, 49 ksec, thin filter, observation ID 0206610101). |
All of these observations have been processed as part of the 2NAIAG catalog (Watsonetal.20093. | All of these observations have been processed as part of the 2XMMi catalog \citep{wat09}. |
.. Note that jpeline products like spectra anne heht curves or all catalog sources can be downloaded frou a dedicatedwebsite. | Note that pipeline products like spectra and light curves for all catalog sources can be downloaded from a dedicated. |
The good time intervals for hese observations amount to observing tines of 15.2 ksec for 559. [3.8 ksec for the PAIR. and Lis ksec for 668. | The good time intervals for these observations amount to observing times of 48.2 ksec for 59, 43.8 ksec for the PMR, and 44.8 ksec for 68. |
The energy range accessible to aud used for the 2NMMIB catalog is wider than the one of ROSAT: it spans 0.212 keV. Tn the following. we mainly work with this catalog. but we have also reprocessed the data using SAS 8.0.0 to subsequently rin our own source detection using the SAS task ewavelet. | The energy range accessible to and used for the 2XMMi catalog is wider than the one of ROSAT; it spans 0.2–12 keV. In the following, we mainly work with this catalog, but we have also reprocessed the data using SAS 8.0.0 to subsequently run our own source detection using the SAS task ewavelet. |
We also ciplov the SAS task especget to xoduce X-ray. spectra of selected sources. | We also employ the SAS task especget to produce X-ray spectra of selected sources. |
For this purpose. we mostly use the EPIC-pu data oulx. rather iu EPICMOS data. apart from the unresolved sources [DIIB2007 1&22 (Brookeetal.2007) which are so fay off-axis (r=11/9) that they are oulv detected with the EPIC-MOS detectors. | For this purpose, we mostly use the EPIC-pn data only, rather than EPIC-MOS data, apart from the unresolved sources [BHB2007] 2 \citep{bro07} which are so far off-axis $r=11\farcm9$ ) that they are only detected with the EPIC-MOS detectors. |
Typically. spectra were extracted feoni areas with a radius of 25" and smalarlw sized. uearby background regious. | Typically, spectra were extracted from areas with a radius of $''$ and similarly sized, nearby background regions. |
The only exception is the close pair. [BITB 2007] 6 T. where we chose a radius of 10” in au attempt to separate the two compoucuts. | The only exception is the close pair [BHB 2007] 6 7, where we chose a radius of $''$ in an attempt to separate the two components. |
The task especect produces the corresponding ancillary response aud response niatrix files. | The task especget produces the corresponding ancillary response and response matrix files. |
Spectra were finally biuned with munimuun bin sizes of 20 counts. | Spectra were finally binned with minimum bin sizes of 20 counts. |
Fits were carried out using the CIAO toolSherpa... V3.1 (Freemanctal.2001). | Fits were carried out using the CIAO tool, V3.4 \citep{fre01}. |
Tn order to assess the mfrared spectral cuerey distributions of selected sources. we have performed. aperture photometry on Spitzer--IRAC data covering the region. most notably observation IDs 5132288. 11089172. and 11090196. | In order to assess the infrared spectral energy distributions of selected sources, we have performed aperture photometry on -IRAC data covering the region, most notably observation IDs 5132288, 14089472, and 14090496. |
For this purpose. we have used pipeline PBCD data from the archive. | For this purpose, we have used pipeline PBCD data from the archive. |
The typical aperture radius was 3 mage pixels with au aunulus for background subtraction with inner aud outer radii of LO aud 20 pixels. | The typical aperture radius was 3 image pixels with an annulus for background subtraction with inner and outer radii of 10 and 20 pixels. |
We have additionally used Spitzer--MIPS data as discussed in Forbricheal.(2009). | We have additionally used -MIPS data as discussed in \citet{for09}. |
. The area covered iu our mnüddnfrared survey (Forbrichetal.2009.Fig.8) contains Ll ROSAT A]LSkv Survev sources. ic. 12 and 32 sources from the Dright aud Faint Source Catalogi"xL respectively, | The area covered in our mid-infrared survey \citep[][Fig.~8]{for09} contains 44 ROSAT All-Sky Survey sources, i.e., 12 and 32 sources from the Bright and Faint Source Catalogues, respectively. |
The locations of these sources are shown in Figure 1.. overlaid on au extinction map of the Pipe Nebula. | The locations of these sources are shown in Figure \ref{fig_rosat}, overlaid on an extinction map of the Pipe Nebula. |
Caven typical lo positional uncertainties of ~20". it is nearly impossible to reliably identify ucarAufrared or optical counterparts to ROSAT N-vay sources in this region with its hieh density of backeround sources. simply due to confusion. | Given typical $1\sigma$ positional uncertainties of $\sim20''$, it is nearly impossible to reliably identify near-infrared or optical counterparts to ROSAT X-ray sources in this region with its high density of background sources, simply due to confusion. |
While this is somewhat easier at | While this is somewhat easier at |
studies of ambipolar cilfusion in the interstellar medium (Mouschovias&Paleologou1981:Shu1983:Brandenburg&Zweibel 1994).. although some of the assumptions ciller rom case to case. | studies of ambipolar diffusion in the interstellar medium \citep{MouschoviasPaleologou81,Shu-83,BZ-94}, although some of the assumptions differ from case to case. |
In. our analysis. we consider separately wo relevant limits. similar in spirit. though not exactly equivalent to those of Mouschovias&Paleologou(1981): For each of these cases. we find that the lone-term evolution of the magnetic field can be mocdelled by a single equation that gives the time-derivative 0D/06 at a given instant / only in terms of the configuration of the magnetic fick at the same instant. Dr./£). | In our analysis, we consider separately two relevant limits, similar in spirit, though not exactly equivalent to those of \citet{MouschoviasPaleologou81}: For each of these cases, we find that the long-term evolution of the magnetic field can be modelled by a single equation that gives the time-derivative $\partial B/\partial t$ at a given instant $t$ only in terms of the configuration of the magnetic field at the same instant, $B(x,t)$. |
This makes it easy to carry out numerical simulations of the evolution of some selected non-linear magnetic field. profiles. and even find some exact. analvtical solutions. | This makes it easy to carry out numerical simulations of the evolution of some selected non-linear magnetic field profiles, and even find some exact, analytical solutions. |
1n Sect. | In Sect. |
2 of this paper. we brielly review the one-dimensional model of neutron star magnetic field evolution introduced. in Paper 1. paving particular attention to its characteristic evolutionary time-scales. | \ref{1dmodel} of this paper, we briefly review the one-dimensional model of neutron star magnetic field evolution introduced in Paper I, paying particular attention to its characteristic evolutionary time-scales. |
In Sects. | In Sects. |
3. and 4.. we obtain the equations for the long-term. asvmptotic magnetic field. evolution promoted by anmbipolar cillusion in cach of the two opposite reginies mentioned above. and we make numerical simulations of the evolution of dillerent initial magnetic field. configurations. | \ref{asy1} and \ref{asy2}, we obtain the equations for the long-term, asymptotic magnetic field evolution promoted by ambipolar diffusion in each of the two opposite regimes mentioned above, and we make numerical simulations of the evolution of different initial magnetic field configurations. |
We show that. in both cases. the magnetic [lux of a given sign tends to spread. out. but singularities develop at the null points where regions with cdillerent signs meet. as oeviouslv found by Brandenburg&Zweibel(1994). | We show that, in both cases, the magnetic flux of a given sign tends to spread out, but singularities develop at the null points where regions with different signs meet, as previously found by \citet{BZ-94}. |
. In he weak coupling case. these singularities correspond. to current sheets that are clissipatecl by resistive effects. in his wav leading to reconnection. | In the weak coupling case, these singularities correspond to current sheets that are dissipated by resistive effects, in this way leading to reconnection. |
In the strong coupling case. the singularities have à somewhat cdillerent character (à smoothly diverging current density) and might lead directly ο reconnection even in the case of no ohmic resistivity (but see Lleitseh&Zweibel 2003a.b)). | In the strong coupling case, the singularities have a somewhat different character (a smoothly diverging current density) and might lead directly to reconnection even in the case of no ohmic resistivity (but see \citealp{H-03a,H-03b}) ). |
Finally. in Sect. 5.0 | Finally, in Sect. \ref{conc}, |
we give he main conclusions of our studv. | we give the main conclusions of our study. |
We model the neutron star interior as an electrically neutral and slightly. ionizecl plasma. composed. of. three mobile. strongly degenerate. particle species: neutrons (n). protons (p). and electrons (ο). | We model the neutron star interior as an electrically neutral and slightly ionized plasma composed of three mobile, strongly degenerate, particle species: neutrons $(n)$, protons $(p)$, and electrons $(e)$. |
We account for binary collisions ancl weak interactions (causing nuclear beta decavs) between he particles. and allow for strong interactions between neutrons and protons by writing each of their. chemical »otentials as a function of both of their number densities: Πριν=μηνny). while considering the electrons as an ideal. relativistic Fermi gas. whose chemical potential is à ‘unction only of their number density. (4—pnQn). | We account for binary collisions and weak interactions (causing nuclear beta decays) between the particles, and allow for strong interactions between neutrons and protons by writing each of their chemical potentials as a function of both of their number densities: $\mu_{n,p}=\mu_{n,p}(n_n,n_p)$, while considering the electrons as an ideal, relativistic Fermi gas, whose chemical potential is a function only of their number density, $\mu_e=\mu_e(n_e)$. |
We study à one-dimensional geometry in which the magnetic field points in one Cartesian direction z. but varies only along an orthogonal direction .r às DU.)= and assume that all physical variables vary only along wr. | We study a one-dimensional geometry in which the magnetic field points in one Cartesian direction $z$, but varies only along an orthogonal direction $x$ as $\vec{B}(\vec{r},t)=B(x,t)\hat{z}$ , and assume that all physical variables vary only along $x$. |
Since. in neutron star conditions. the ratio of the magnetic pressure J7/8x to the pressure of the charged particles is very small. the magnetic force causes only small perturbations to the hyelrostatic equilibrium state of the non-magnetized star. | Since, in neutron star conditions, the ratio of the magnetic pressure $B^2/8\pi$ to the pressure of the charged particles is very small, the magnetic force causes only small perturbations to the hydrostatic equilibrium state of the non-magnetized star. |
‘These assumptions are generally not true in molecular cloud. cores. where the ionization [raction tends to be extremely low. whereas the magnetic Ποιά can be near equipartition with the neutral eas pressure. | These assumptions are generally not true in molecular cloud cores, where the ionization fraction tends to be extremely low, whereas the magnetic field can be near equipartition with the neutral gas pressure. |
In this sense. our derivation will be valid. only for the case of neutron stars. although we will sec that some of the results agree with those of other authors. obtained under. somewhat diferent assumptions. | In this sense, our derivation will be valid only for the case of neutron stars, although we will see that some of the results agree with those of other authors, obtained under somewhat different assumptions. |
more general treatment appears to be dillicult and not to vield simple results. | A more general treatment appears to be difficult and not to yield simple results. |
For the reasons stated. we consider à non-magnetized. fixed background. system in hwdrostatic and chemical equilibrium and introduce. small perturbations to. the number density. of cach species / as miGr1)τμ.)|δη(μην D. with the subscript zero labelling the background number densities and. [ωνD|«πιω. | For the reasons stated, we consider a non-magnetized, fixed background system in hydrostatic and chemical equilibrium and introduce small perturbations to the number density of each species $i$ as $n_i(x,t)= n_{0i}(x)+\delta n_i(x,t)$ , with the subscript zero labelling the background number densities and $|\delta n_i(x,t)|\ll n_{0i}(x)$. |
“Phe associated chemical potential perturbations are given by f/n=fto;|0405. | The associated chemical potential perturbations are given by $\mu_{i}=\mu_{0i}+\delta
\mu_{i}$. |
The long-term magnetic field. evolution. implies. small particle velocities that change over long time-scales. much longer than the very short dvnamical times that are only relevant shortly after the formation of the star (L6. sound or Alfvénn time-scales). | The long-term magnetic field evolution implies small particle velocities that change over long time-scales, much longer than the very short dynamical times that are only relevant shortly after the formation of the star (i.e, sound or Alfvénn time-scales). |
Therefore. at all times we use a slow-motion approximation in which we neglect the acceleration terms in the equations of motion for the ‘Taking account of all these considerations. the svsteni of non-lincar partial differential equations governing the evolution is (see Paper I for the derivation) where and | Therefore, at all times we use a slow-motion approximation in which we neglect the acceleration terms in the equations of motion for the Taking account of all these considerations, the system of non-linear partial differential equations governing the evolution is (see Paper I for the derivation) where and |
dispersion in age. | dispersion in age. |
It is further assumed that all stars begin their lives with a disc and that the disc lifetime is drawn from an exponentially decaying distribution with a characteristic timescale of MMyr. | It is further assumed that all stars begin their lives with a disc and that the disc lifetime is drawn from an exponentially decaying distribution with a characteristic timescale of Myr. |
Different functional forms for these distributions are possible and will be explored in Section 4. | Different functional forms for these distributions are possible and will be explored in Section 4. |
The three panels of Fig. | The three panels of Fig. |
1 show, for simulated populations of 300000 stars, how the observed (or apparent) age distributions for stars with and without discs become clearly separated when the dispersion in real ages becomes large enough that there are many stars older than 3MMyr that have a high probability of having lost their discs. | \ref{showmodel} show, for simulated populations of 000 stars, how the observed (or apparent) age distributions for stars with and without discs become clearly separated when the dispersion in real ages becomes large enough that there are many stars older than Myr that have a high probability of having lost their discs. |
There have been a number of previous attempts to identify this phenomenon with mixed outcomes. | There have been a number of previous attempts to identify this phenomenon with mixed outcomes. |
? found that there was considerable overlap of stars with and without near-infrared excess in the HR diagram of the Taurus-Auriga association, but that the stars presumed to be discless were older on average. | \citet{strom89} found that there was considerable overlap of stars with and without near-infrared excess in the HR diagram of the Taurus-Auriga association, but that the stars presumed to be discless were older on average. |
Subsequently, ? and ? found that classical T-Tauri stars (CTTS) with veiling and accretion discs were systematically younger than their discless, weak-lined T-Tauri star (WTTS) counterparts in the Taurus-Auriga association. | Subsequently, \citet{hartigan95} and \citet{bertout07} found that classical T-Tauri stars (CTTS) with veiling and accretion discs were systematically younger than their discless, weak-lined T-Tauri star (WTTS) counterparts in the Taurus-Auriga association. |
These samples were relatively small and it is likely that X-ray selected foreground field stars contaminated the WTTS samples, making them appear older. | These samples were relatively small and it is likely that X-ray selected foreground field stars contaminated the WTTS samples, making them appear older. |
? observed CTTS and WTTS in the L1630 and L1641 clouds, finding some evidence for a decrease with age in disc frequency determined from infrared excesses, and a 97 per cent signficance result that CTTS and WTTS were not drawn from the same age distribution. | \citet{fang09} observed CTTS and WTTS in the L1630 and L1641 clouds, finding some evidence for a decrease with age in disc frequency determined from infrared excesses, and a 97 per cent signficance result that CTTS and WTTS were not drawn from the same age distribution. |
On the other hand ?,, ?,, ? and ? all found no difference in the age distributions of CTTS and WTTS in the 3348, 55146, NGC 2264 and c Orionis clusters respectively. | On the other hand \citet{herbig98}, \citet{herbig02}, \citet{dahm05} and \citet{rigliaco11} all found no difference in the age distributions of CTTS and WTTS in the 348, 5146, NGC 2264 and $\sigma$ Orionis clusters respectively. |
The goal of this investigation is to search for differences in the age distributions of stars with and without discs in a large and homogeneous sample from the ONC, and thus estimate the extent of any real age spread. | The goal of this investigation is to search for differences in the age distributions of stars with and without discs in a large and homogeneous sample from the ONC, and thus estimate the extent of any real age spread. |
The observational basis is the optical catalogue and HR diagram of the ONC produced by DR10. | The observational basis is the optical catalogue and HR diagram of the ONC produced by DR10. |
This improves on earlier work by ? and is the largest homogeneous catalogue of photometry and spectral types for stars in the ONC. | This improves on earlier work by \citet{hillenbrand97} and is the largest homogeneous catalogue of photometry and spectral types for stars in the ONC. |
DR10 simultaneously used photometry and spectroscopy to estimate extinction and accretion luminosity and hence find the intrinsic bolometric luminosity and effective temperature for each source. | DR10 simultaneously used photometry and spectroscopy to estimate extinction and accretion luminosity and hence find the intrinsic bolometric luminosity and effective temperature for each source. |
The sample of ONC stars was filtered to exclude possible non-members with membership probabilities based | The sample of ONC stars was filtered to exclude possible non-members with membership probabilities based |
Cepheid ciameters. | Cepheid diameters. |
ILowever. (hey find (hat infrared photometry (Uv.—A) is less sensitive to the effects of gravity. and microturbulence (and presumably. also redcdening). aud. hence vields more accurate results. | However, they find that infrared photometry $K, J-K$ ) is less sensitive to the effects of gravity and microturbulence (and presumably also reddening), and hence yields more accurate results. |
For shorter periods (<11.8 davs) their resulüs indicate smaller diameters as compared to other relations. | For shorter periods $\le 11.8$ days) their results indicate smaller diameters as compared to other relations. |
Given the limited sample of only (wo radius measurements we can draw only preliminary conclusions: (1) ihe general agreement between our observations and (he relations is good. and (2) the data seem (o prefer a shallower slope than (the Laney&Stlobie(1995) relation. | Given the limited sample of only two radius measurements we can draw only preliminary conclusions: (1) the general agreement between our observations and the relations is good, and (2) the data seem to prefer a shallower slope than the \citet{laney95} relation. |
This latter observation will have to be confirmed with observations ofshorter-period Cepheids. | This latter observation will have to be confirmed with observations of shorter-period Cepheids. |
We have measured the changes in angular diameter of two Cepheids. η Aq] and à Gem. using PTI. | We have measured the changes in angular diameter of two Cepheids, $\eta$ Aql and $\zeta$ Gem, using PTI. |
When combined with previously published radial velocity data we can derive the distance and mean diameter to the Cepheids. | When combined with previously published radial velocity data we can derive the distance and mean diameter to the Cepheids. |
We find 77 Aq to be at a distance of 8320432 pe with a mean raclius of 61.521.64... | We find $\eta$ Aql to be at a distance of $320 \pm 32$ pc with a mean radius of $61.8 \pm 7.6 R_{\odot}$. |
We find ¢ Gem to be at a distance of 362238 pe. wilh a mean radius of 66.757.2. . in good agreement wilh previous work. | We find $\zeta$ Gem to be at a distance of $ 362\pm38$ pc, with a mean radius of $ 66.7\pm7.2 R_{\odot}$ , in good agreement with previous work. |
The precision achieved js e in the parameters: further improvement is al present limited by our understanding of the details o “the Cepheid atmospheres. | The precision achieved is $\sim$ in the parameters; further improvement is at present limited by our understanding of the details of the Cepheid atmospheres. |
In particular the details of limb darkening and projection [actors need to be understood. with the projection [actors being (he largest source ol svsteniatic τι1certanlv. | In particular the details of limb darkening and projection factors need to be understood, with the projection factors being the largest source of systematic uncertainty. |
We note thal (hese results do not rely on photometric surface brightness relations. hence results derived rere can be used (to calibrate such relations. | We note that these results do not rely on photometric surface brightness relations, hence results derived here can be used to calibrate such relations. |
We performed such calibrations and found: goo«| agreement with previous results. | We performed such calibrations and found good agreement with previous results. |
We also note (hal al present we have derived distances to only (wo Cepheids. and although (he derived distances areconsistent | We also note that at present we have derived distances to only two Cepheids, and although the derived distances areconsistent |
In this section we suppose there is an unidentified transition. arising from some species in the same gas cloud as is being studied. | In this section we suppose there is an unidentified transition, arising from some species in the same gas cloud as is being studied. |
We further assume that this interloping transition is not strong enough and/or sullicicntly clisplaced from one of the lines in the analysis. to be detected directly. | We further assume that this interloping transition is not strong enough and/or sufficiently displaced from one of the lines in the analysis, to be detected directly. |
We describe two approaches to explore this: in Section 4.1 we attempt to identify candidate blending species and in section 4.2 we describe the results of à test where we remove one Lransition or one species at à time to investigate the impact on zNafa. | We describe two approaches to explore this: in Section 4.1 we attempt to identify candidate blending species and in Section 4.2 we describe the results of a test where we remove one transition or one species at a time to investigate the impact on $\da$. |
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