<?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>S0185-11012016000200419</article-id>
<title-group>
<article-title xml:lang="en"><![CDATA[The primordial helium abundance and the number of neutrino families]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Peimbert]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Peimbert]]></surname>
<given-names><![CDATA[M.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Luridiana]]></surname>
<given-names><![CDATA[V.]]></given-names>
</name>
<xref ref-type="aff" rid="Aff"/>
<xref ref-type="aff" rid="Aaf"/>
</contrib>
</contrib-group>
<aff id="Af1">
<institution><![CDATA[,Universidad Nacional Autónoma de México Instituto de Astronomía ]]></institution>
<addr-line><![CDATA[ ]]></addr-line>
<country>Mexico</country>
</aff>
<aff id="Af2">
<institution><![CDATA[,Instituto de Astrofísica de Canarias  ]]></institution>
<addr-line><![CDATA[ ]]></addr-line>
<country>Spain</country>
</aff>
<aff id="Af3">
<institution><![CDATA[,Universidad de La Laguna Departamento de Astrofísica ]]></institution>
<addr-line><![CDATA[ ]]></addr-line>
<country>Spain</country>
</aff>
<pub-date pub-type="pub">
<day>00</day>
<month>00</month>
<year>2016</year>
</pub-date>
<pub-date pub-type="epub">
<day>00</day>
<month>00</month>
<year>2016</year>
</pub-date>
<volume>52</volume>
<numero>2</numero>
<fpage>419</fpage>
<lpage>424</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_arttext&amp;pid=S0185-11012016000200419&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_abstract&amp;pid=S0185-11012016000200419&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_pdf&amp;pid=S0185-11012016000200419&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="en"><p><![CDATA[Abstract: Based on observations of H II regions and on the new computations of the recombination coefficients of the He I lines by Porter el al. we obtain a primordial helium abundance by mass of YP = 0.2446 ± 0.0029. We consider thirteen sources of error for the YP determination; some of them are mainly due to systematic effects, while the rest are mainly due to statistical effects. We compare our results with other determinations of YP present in the literature. Combining our YP value with computations of primordial nucleosynthesis we find a number of neutrino species Neff = 2.90 ± 0.22, and a neutron mean life &#964;&#957; = 872 ± 14 s.]]></p></abstract>
<abstract abstract-type="short" xml:lang="es"><p><![CDATA[Resumen: Basados en observaciones de regiones H II y en los nuevos cálculos de los coeficientes de recombinación de las líneas de He I debidos a Porter et al. obtenemos una abundancia primordial de helio por unidad de masa dada por YP = 02446 ± 0.0029. Consideramos trece fuentes de error en la determinación de YP; algunas de ellas se deben principalmente a efectos sistemáticos mientras que el resto se deben principalmente a efectos estadísticos. Comparamos nuestros resultados con otros valores de YP determinados por otros grupos. Combinando nuestro valor de YP con cálculos de nucleosíntesis primordial encontramos que el número efectivo de familias de neutrinos, Neff, es de 2.90 ± 0.22 y que la vida media del neutrón, &#964;&#957; es de 872 ± 14 s.]]></p></abstract>
<kwd-group>
<kwd lng="en"><![CDATA[early universe]]></kwd>
<kwd lng="en"><![CDATA[galaxies: abundances]]></kwd>
<kwd lng="en"><![CDATA[galaxies: ISM]]></kwd>
<kwd lng="en"><![CDATA[H II regions]]></kwd>
<kwd lng="en"><![CDATA[ISM: abundances]]></kwd>
</kwd-group>
</article-meta>
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