Show Author in custom rss feed

I am using the code from yoast https://yoast.com/tag/rss/ and have modified it a bit to show the featured image which it is doing. I am trying to figure out how to show the Author now

I tried adding int

but that does not work. What am I missing to get this to show?

<?php
/*
Template Name: Custom Feed
*/

$numposts = 10;

function acustom_rss_date( $timestamp = null ) {
$timestamp = ($timestamp==null) ? time() : $timestamp;
echo date(DATE_RSS, $timestamp);
}

function acustom_rss_text_limit($string, $length, $replacer="...") { 
$string = strip_tags($string);
if(strlen($string) > $length) 
return (preg_match('/^(.*)\W.*$/', substr($string, 0, $length+1), $matches)  ? $matches[1] : substr($string, 0, $length)) . $replacer;   
return $string; 
}

$posts = query_posts('showposts=".$numposts);

$lastpost = $numposts - 1;

header("Content-Type: application/rss+xml; charset=UTF-8");
echo "<?xml version="1.0"?>';
?><rss version="2.0" xmlns:media="http://search.yahoo.com/mrss">
<channel>
<title>Test E-mail Update</title>
<link>http://www.test.com/</link>
<description>The latest posts from test.com</description>
<language>en-us</language>
<pubDate><?php acustom_rss_date( strtotime($ps[$lastpost]->post_date_gmt) ); ?></pubDate>
<lastBuildDate><?php acustom_rss_date( strtotime($ps[$lastpost]- >post_date_gmt) ); ?></lastBuildDate>
<?php foreach ($posts as $post) { ?>
<item>
<title><?php echo get_the_title($post->ID); ?></title>
<link><?php echo get_permalink($post->ID); ?></link>
 <?php if(get_the_post_thumbnail()): ?>
<media:content url="<?php $image =   wp_get_attachment_image_src(get_post_thumbnail_id($post->ID), 'thumbnail'); echo  $image[0]; ?>" medium="image" />
<?php endif; ?>

<description>


<?php echo '<![CDATA['.acustom_rss_text_limit($post->post_content, 500).'<br/><br/><a href="'.get_permalink($post->ID).'"> Continue Reading. </a>'.']]>';  ?>



</description>


<dc:creator><?php echo get_the_author_meta( 'display_name', $post->post_author ); ?>

<pubDate><?php acustom_rss_date( strtotime($post->post_date_gmt) ); ?></pubDate>
<guid><?php echo get_permalink($post->ID); ?></guid>
</item>
<?php } ?>
</channel>
</rss>

Try it:

<?php echo get_the_author_meta( 'display_name', $post->post_author ); ?>

You can use the_author function in wordpress standard loop, Not foreach. to set global author information you should use the_post function. but in foreach, you can use get_the_author_meta instead of the_author to pass author id $post->post_author.