<?xml version="1.0" encoding="ISO-8859-1"?><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<front>
<journal-meta>
<journal-id>0185-1101</journal-id>
<journal-title><![CDATA[Revista mexicana de astronomía y astrofísica]]></journal-title>
<abbrev-journal-title><![CDATA[Rev. mex. astron. astrofis]]></abbrev-journal-title>
<issn>0185-1101</issn>
<publisher>
<publisher-name><![CDATA[Universidad Nacional Autónoma de México, Instituto de Astronomía]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S0185-11012015000100007</article-id>
<title-group>
<article-title xml:lang="en"><![CDATA[A new approximate analytic solution for the ionization structure of a Strömgren sphere]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Raga]]></surname>
<given-names><![CDATA[A. G.]]></given-names>
</name>
<xref ref-type="aff" rid="A01"/>
</contrib>
</contrib-group>
<aff id="A01">
<institution><![CDATA[,Universidad Nacional Autónoma de México Instituto de Ciencias Nucleares ]]></institution>
<addr-line><![CDATA[México Distrito Federal]]></addr-line>
<country>México</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>00</month>
<year>2015</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>00</month>
<year>2015</year>
</pub-date>
<volume>51</volume>
<numero>1</numero>
<fpage>59</fpage>
<lpage>63</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_arttext&amp;pid=S0185-11012015000100007&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_abstract&amp;pid=S0185-11012015000100007&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_pdf&amp;pid=S0185-11012015000100007&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="es"><p><![CDATA[(Strömgren 1939) presentó un modelo para la fotoionización de una nebulosa homogénea, y derivó soluciones analíticas aproximadas de su modelo. El presente artículo explora el modelo de Strömgren y muestra que es posible construir soluciones analíticas más precisas (aunque por supuesto más complejas). Estas soluciones son interesantes para inicializar simulaciones numéricas y para tener una descripción analítica adecuada de regiones fotoionizadas con zonas transición HII&#8594;HI "gruesas".]]></p></abstract>
<abstract abstract-type="short" xml:lang="en"><p><![CDATA[(Strömgren 1939) presented a model for the photoionization of a homogeneous nebula, and derived approximate analytic solutions to his model. The present paper explores Strömgren's model, and shows that it is possible to construct more accurate (though of course more complex) analytic solutions. These new solutions are interesting for initializing numerical simulations and for obtaining an appropriate analytic description of photoionized regions with "thick" HII&#8594;HI transition regions.]]></p></abstract>
<kwd-group>
<kwd lng="en"><![CDATA[ISM]]></kwd>
</kwd-group>
</article-meta>
</front><body><![CDATA[  	    <p align="center"><font face="verdana" size="4"><b>A new approximate analytic solution for the ionization structure of a Str&ouml;mgren sphere</b></font></p>  	    <p align="center"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="center"><font face="verdana" size="2"><b>A. G. Raga</b></font></p>  	    <p align="center"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><i>Instituto de Ciencias Nucleares, Universidad Nacional Aut&oacute;noma de M&eacute;xico, Apdo. Postal 70&#45;543, C. P. 04510, M&eacute;xico, D. F., M&eacute;xico</i> (<a href="mailto:raga@nucleares.unam.mx">raga@nucleares.unam.mx</a>).</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2">Received April 1 2014.    <br> 	Accepted September 2 2014.</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    ]]></body>
<body><![CDATA[<p align="justify"><font face="verdana" size="2"><b>RESUMEN</b></font></p>  	    <p align="justify"><font face="verdana" size="2">(Str&ouml;mgren 1939) present&oacute; un modelo para la fotoionizaci&oacute;n de una nebulosa homog&eacute;nea, y deriv&oacute; soluciones anal&iacute;ticas aproximadas de su modelo. El presente art&iacute;culo explora el modelo de Str&ouml;mgren y muestra que es posible construir soluciones anal&iacute;ticas m&aacute;s precisas (aunque por supuesto m&aacute;s complejas). Estas soluciones son interesantes para inicializar simulaciones num&eacute;ricas y para tener una descripci&oacute;n anal&iacute;tica adecuada de regiones fotoionizadas con zonas transici&oacute;n HII&#8594;HI "gruesas".</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>ABSTRACT</b></font></p>  	    <p align="justify"><font face="verdana" size="2">(Str&ouml;mgren 1939) presented a model for the photoionization of a homogeneous nebula, and derived approximate analytic solutions to his model. The present paper explores Str&ouml;mgren's model, and shows that it is possible to construct more accurate (though of course more complex) analytic solutions. These new solutions are interesting for initializing numerical simulations and for obtaining an appropriate analytic description of photoionized regions with "thick" HII&#8594;HI transition regions.</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>Key Words:</b> ISM: HII regions.</font></p> 	    <p align="justify">&nbsp;</p>  	    <p align="justify"><font face="verdana" size="2"> <a href="/pdf/rmaa/v51n1/v51n1a7.pdf" target="_blank">DESCARGAR ART&Iacute;CULO EN FORMATO PDF</a></font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>ACKNOWLEDGMENT</b></font></p>  	    ]]></body>
<body><![CDATA[<p align="justify"><font face="verdana" size="2">We acknowledge support from the CONACyT grants 61547, 101356, 101975 and 167611 and the DGAPA&#45;UNAM grants IN105312 and IG100214.</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>REFERENCES</b></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">Binette, L. 1985, A &amp; A, 143, 334</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=7447348&pid=S0185-1101201500010000700001&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --><!-- ref --><p align="justify"><font face="verdana" size="2">Binette, L., Wang, J., Villar&#45;Mart&iacute;n, M., Martin, P. G., Magris, C. G. 1993, ApJ, 414, 535 Draine,    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=7447349&pid=S0185-1101201500010000700002&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --><!-- ref --> B. T. 2011, ApJ, 732, 100</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=7447350&pid=S0185-1101201500010000700003&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --><!-- ref --><p align="justify"><font face="verdana" size="2">Dyson, J. E., Williams, D. A. 1980, "The Physics of the Interstellar Medium", Manchester University Press, Manchester</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=7447351&pid=S0185-1101201500010000700004&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --><!-- ref --><p align="justify"><font face="verdana" size="2">Halpern, J. P., Steiner, J. E. 1983, ApJ, 269, L37</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=7447352&pid=S0185-1101201500010000700005&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --><!-- ref --><p align="justify"><font face="verdana" size="2">Petrosian, V., Silk, J., Field, G. B. 1977, ApJ, 177, L69</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=7447353&pid=S0185-1101201500010000700006&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --><!-- ref --><p align="justify"><font face="verdana" size="2">Str&ouml;mgren, B. 1939, ApJ, 89, 526</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=7447354&pid=S0185-1101201500010000700007&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --><!-- ref --><p align="justify"><font face="verdana" size="2">Tremblin, P., Audit, E., Minier, V., Schmidt, W., Schneider, N. 2012, A &amp; A, 546, 33</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=7447355&pid=S0185-1101201500010000700008&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --> ]]></body><back>
<ref-list>
<ref id="B1">
<nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Binette]]></surname>
<given-names><![CDATA[L.]]></given-names>
</name>
</person-group>
<source><![CDATA[A & A]]></source>
<year>1985</year>
<volume>143</volume>
<page-range>334</page-range></nlm-citation>
</ref>
<ref id="B2">
<nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Binette]]></surname>
<given-names><![CDATA[L.]]></given-names>
</name>
<name>
<surname><![CDATA[Wang]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
<name>
<surname><![CDATA[Villar-Martín]]></surname>
<given-names><![CDATA[M.]]></given-names>
</name>
<name>
<surname><![CDATA[Martin]]></surname>
<given-names><![CDATA[P. G.]]></given-names>
</name>
<name>
<surname><![CDATA[Magris]]></surname>
<given-names><![CDATA[C. G.]]></given-names>
</name>
</person-group>
<source><![CDATA[ApJ]]></source>
<year>1993</year>
<volume>414</volume>
<page-range>535</page-range></nlm-citation>
</ref>
<ref id="B3">
<nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Draine]]></surname>
<given-names><![CDATA[B. T.]]></given-names>
</name>
</person-group>
<source><![CDATA[ApJ]]></source>
<year>2011</year>
<volume>732</volume>
<page-range>100</page-range></nlm-citation>
</ref>
<ref id="B4">
<nlm-citation citation-type="book">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Dyson]]></surname>
<given-names><![CDATA[J. E.]]></given-names>
</name>
<name>
<surname><![CDATA[Williams]]></surname>
<given-names><![CDATA[D. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[The Physics of the Interstellar Medium]]></source>
<year>1980</year>
<publisher-loc><![CDATA[Manchester ]]></publisher-loc>
<publisher-name><![CDATA[Manchester University Press]]></publisher-name>
</nlm-citation>
</ref>
<ref id="B5">
<nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Halpern]]></surname>
<given-names><![CDATA[J. P.]]></given-names>
</name>
<name>
<surname><![CDATA[Steiner]]></surname>
<given-names><![CDATA[J. E.]]></given-names>
</name>
</person-group>
<source><![CDATA[ApJ]]></source>
<year>1983</year>
<volume>269</volume>
<page-range>L37</page-range></nlm-citation>
</ref>
<ref id="B6">
<nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Petrosian]]></surname>
<given-names><![CDATA[V.]]></given-names>
</name>
<name>
<surname><![CDATA[Silk]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
<name>
<surname><![CDATA[Field]]></surname>
<given-names><![CDATA[G. B.]]></given-names>
</name>
</person-group>
<source><![CDATA[ApJ]]></source>
<year>1977</year>
<volume>177</volume>
<page-range>L69</page-range></nlm-citation>
</ref>
<ref id="B7">
<nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Strömgren]]></surname>
<given-names><![CDATA[B.]]></given-names>
</name>
</person-group>
<source><![CDATA[ApJ]]></source>
<year>1939</year>
<volume>89</volume>
<page-range>526</page-range></nlm-citation>
</ref>
<ref id="B8">
<nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Tremblin]]></surname>
<given-names><![CDATA[P.]]></given-names>
</name>
<name>
<surname><![CDATA[Audit]]></surname>
<given-names><![CDATA[E.]]></given-names>
</name>
<name>
<surname><![CDATA[Minier]]></surname>
<given-names><![CDATA[V.]]></given-names>
</name>
<name>
<surname><![CDATA[Schmidt]]></surname>
<given-names><![CDATA[W.]]></given-names>
</name>
<name>
<surname><![CDATA[Schneider]]></surname>
<given-names><![CDATA[N.]]></given-names>
</name>
</person-group>
<source><![CDATA[A & A]]></source>
<year>2012</year>
<volume>546</volume>
<page-range>33</page-range></nlm-citation>
</ref>
</ref-list>
</back>
</article>
