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We make use of ALMA continuum observations of $15$ luminous Lyman-breakgalaxies at $z$$\sim$$7$$-$$8$ to probe their dust-obscured star-formation.These observations are sensitive enough to probe to obscured SFRs of $20$$M_{\odot}$$/$$yr$ ($3\sigma$). Six of the targeted galaxies show significant($\geq$$3$$\sigma$) dust continuum detections, more than doubling the number ofknown dust-detected galaxies at $z$$>$$6.5$. Their IR luminosities range from$2.7$$\times$$10^{11}$ $L_{\odot}$ to $1.1$$\times$$10^{12}$ $L_{\odot}$,equivalent to obscured SFRs of $20$ to $105$ $M_{\odot}$$/$$yr$. We use ourresults to quantify the correlation of the infrared excess IRX on theUV-continuum slope $\beta_{UV}$ and stellar mass. Our results are mostconsistent with an SMC attenuation curve for intrinsic $UV$-slopes$\beta_{UV,intr}$ of $-2.63$ and most consistent with an attenuation curvein-between SMC and Calzetti for $\beta_{UV,intr}$ slopes of $-2.23$, assuming adust temperature $T_d$ of $50$ K. Our fiducial IRX-stellar mass results at$z$$\sim$$7$$-$$8$ are consistent with marginal evolution from $z$$\sim$$0$. Wethen show how both results depend on $T_d$. For our six dust-detected sources,we estimate their dust masses and find that they are consistent with dustproduction from SNe if the dust destruction is low ($<$$90$%). Finally wedetermine the contribution of dust-obscured star formation to the starformation rate density for $UV$ luminous ($<$$-$$21.5$ mag:$\gtrsim$$1.7$$L_{UV} ^*$) $z$$\sim$$7$$-$$8$ galaxies, finding that the totalSFR density at $z$$\sim$$7$ and $z$$\sim$$8$ from bright galaxies is$0.18_{-0.10}^{+0.08}$ dex and $0.20_{-0.09}^{+0.05}$ dex higher, respectively,i.e. $\sim$$\frac{1}{3}$ of the star formation in $\gtrsim$$1.7$$L_{UV} ^*$galaxies at $z$$\sim$$7$$-$$8$ is obscured by dust.

Significant Dust-Obscured Star Formation in Luminous Lyman-break Galaxies at $z$$\sim$$7$$-$$8$