Description:
<jats:title>Abstract</jats:title>
<jats:p>We present the low-resolution transmission spectra of the puffy hot Jupiter HAT-P-65b (0.53 M<jats:sub>Jup</jats:sub>, 1.89 R<jats:sub>Jup</jats:sub>, <jats:italic>T</jats:italic>
<jats:sub>eq</jats:sub> = 1930 K), based on two transits observed using the OSIRIS spectrograph on the 10.4 m Gran Telescopio CANARIAS. The transmission spectra of the two nights are consistent, covering the wavelength range 517–938 nm and consisting of mostly 5 nm spectral bins. We perform equilibrium-chemistry spectral retrieval analyses on the jointly fitted transmission spectrum and obtain an equilibrium temperature of <jats:inline-formula>
<jats:tex-math>
<?CDATA ${1645}_{-244}^{+255}$?>
</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabfbe1ieqn1.gif" xlink:type="simple" />
</jats:inline-formula> K and a cloud coverage of <jats:inline-formula>
<jats:tex-math>
<?CDATA ${36}_{-17}^{+23}$?>
</jats:tex-math>
<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabfbe1ieqn2.gif" xlink:type="simple" />
</jats:inline-formula>%, revealing a relatively clear planetary atmosphere. Based on free-chemistry retrieval, we report strong evidence for titanium oxide (TiO). Additional individual analyses in each night reveal weak-to-moderate evidence for TiO in both nights, but moderate evidence for Na or VO only in one of the nights. Future high-resolution Doppler spectroscopy as well as emission observations will help confirm the presence of TiO and constrain its role in shaping the vertical thermal structure of HAT-P-65b’s atmosphere.</jats:p>