@hikaru29 D1 chart is Lagna or Rasi chart (main birth chart).
D9 is Navamsa
Sidereal is the type of astrology, also known as Vedic. Just like tropical astrology is also known as Western.
D1 chart in Vedic astrology, is sidereal - same with any other Vedic charts. Unless you use vaultofheavens.com - that is all western placements, including the divisional charts.
In my opinion, it makes it more complicated taking Vedic practices and applying it to western astrology - thats why I think its important to look at your Vedic divisional charts if you want to use Vedic practices.
You aren't able to generate a D9 Navamsa chart on astro.com.
I use vedic-horo.com for all divisional charts, it makes it easy for you and shows you the nakshatras for each chart, as well as your dasha period and also how well the planet is doing in each chart.
D1 chart shows you your main path in this lifetime.
D9 chart shows you the heart of each planet in your D1 chart.
D12 Dwadadamsa is the DNA of each planet.
And D60 Shashtyamsa becomes the soul of each planet.